Update to 2.10.12

Changelog:
Overview of Changes from GIMP 2.10.10 to GIMP 2.10.12
=====================================================

Core:

  - Add an "Incremental" option to the Dodge/Burn tool, which,
    similarly to the Paintbrush, Pencil, and Eraser tools, applies the
    effect incrementally as the pointer moves.
  - Curves now have a concept of smooth vs corner points: smooth
    points produce a smooth curve, while corner points produce a sharp
    curve (previously, all points were smooth).
  - Search the user font directory path on Windows (since Windows 10,
    non-admin users have the ability to install fonts). This is only a
    temporary hack until fontconfig adds proper upstream support:
    https://gitlab.freedesktop.org/fontconfig/fontconfig/issues/144
  - In gimp_brush_core_get_paint_buffer(), when allocating a new paint
    buffer, clear the old buffer *before* allocating the new one, to
    reduce the amount of simultaneously allocated memory.
  - In GimpPaintbrush, avoid refilling the paint buffer at each dab if
    the paint color/pixmap hasn't changed, hence allowing faster
    painting in some specific cases.
  - Add hygon cpu detection and enable MMX/SSE support.
  - Add a GimpSymmetry::get_transform() virtual function and a
    corresponding gimp_symmetry_get_transform() function which return
    the brush transform corresponding to a given symmetry stroke in
    terms of the rotation angle and reflection flag (in contrast to
    gimp_symmetry_get_operation() which returns the same transforation
    in terms of a GeglNode). This allows us to simplify, fix (artifact
    bugs, etc.), and improve the painting-code performance for several
    symmetry painting cases.
  - New gimp-brush-pipe-spacing parasite set by core code to preserve
    GIH brush's spacing across reloads.
  - Add a new Offset filter tool, as a front-end to gimp:offset. The
    tool replaces, and provides the same interface as the drawable-
    offset dialog while also providing live preview and on-canvas
    interaction.

Plug-ins:

  - Exported profile and data format strategy updated in several file
    plug-ins.

    * When not saving a profile, we always export as sRGB data, as most
      viewers would not display the image properly otherwise.
    * When saving a profile:
        * If a profile was manually assigned, we always export to the
          assigned format, hence pixel data is converted accordingly,
	  whatever the work format.
        * If no profile was assigned:
            * If the export format support high-bit depth, we export the
              work format as-is.
            * If the export format is 8-bit max, we convert the work
              format to sRGB, except if the work format is 8-bit linear.

    The following plug-ins were updated: JPEG, PNG, TIFF and WebP.

  - TIFF plug-in now supports layer export.
  - Add accelerator on "Save color _profile" item in JPEG export so
    that all items in the dialog have keyboard accelerators.
  - Add a "Save color profile" checkbox in WebP export and remove the
    "Advanced Options" expander (all metadata and profile writing
    options are now directly visible).
  - Process cases of non-conformant TIFF file with extra channels
    while ExtraSamples is not set by assuming the first extra channel
    is a non-premultiplied alpha channel and outputting a warning. In
    the future, this should be updated further by a dialog asking what
    to do with the non-defined dialog (consider as premultiplied or
    non-premultiplied alpha channel, or just save as extra channels).

Tools:

  - Add input/output spin-buttons to the Curves tool, which allow
    setting the selected point's coordinates numerically. When the image
    precision is greater than 8-bpc, use a 0.00-100.00 range for the
    point-coordinate spin-buttons instead of a 0-255 range.
  - In the Curves tool, allow changing the curve's point types (cf. new
    curve corner points in Core section). Corner points are displayed
    with a diamond shape instead of a circle.
  - Free Select tool now creates a selection as soon as the polygon is
    closed. This selection is updated when the polygon, or the relevant
    tool-options, change, similarly to GimpRectangleSelectTool.
  - Derive GimpEraser from GimpPaintbrush, instead of directly from
    GimpBrushCore.
    This allows GimpEraser to reuse the paint-buffer content across
    dabs, improving performance.
  - Allow moving an intersecting pair of guides with the Move tool.

User interface:

  - In GimpCurveView, when dragging an existing curve point, don't
    immediately move the point to the cursor position upon button
    press, but rather move it relative to its current position as the
    cursor moves. This allows selecting a point without moving it, and
    adjusting its position more easily.
  - when the cursor hovers above a point in GimpCurveView, or when
    dragging a point, have the coordinate indicator show the point's
    position, rather than the cursor's.
  - In GimpCurveView, when holding down Ctrl while adding/dragging a
    point, snap the y-coordinate to the original curve (at the start
    of the drag). This is particularly useful for adding points along
    the curve.
  - In GimpDashboard, don't show legend for groups with no meter.
  - Add a tile-alloc-total variable to the dashboard's memory and misc
    groups, showing the total amount of memory used by the tile
    allocator.
  - Add a "Save Keyboard Shortcuts Now" button to the Configure
    Keyboard Shortcuts dialog.

Installers:

  - Windows: enable InnoSetup "unofficial" translations. Otherwise we
    had a bunch of wasted work from our translators of several
    languages whose translations were never used in the installer.

Translations:

   - 12 translations were updated: Catalan, Chinese, French, German,
     Hungarian, Indonesian, Italian, Polish, Russian, Spanish, Swedish
     and Turkish.


(ryoon)