indent: extend debug logging for the parser state

The member names in struct parser_state are not trustworthy, for example
in_decl does not correspond to the intuitive definition of "inside a
declaration".  To cope with this uncertainty, output the full state of
the parser state to the debug log, not only the changes.  This helps to
track the inner state for small differences in the input, such as
between 'typedef enum { TA, TB } TT' and 'enum { EA, EB } ET'.

This hopefully helps in fixing PR#55453.

No functional change outside debug mode.

(rillig)