grpc: update to 1.34.0.

This release contains refinements, improvements, and bug fixes,
with highlights listed below.

Core

    Protect xds security code with the environment variable "GRPC_XDS_EXPERIMENTAL_SECURITY_SUPPORT". (#24782)
    Add support for "unix-abstract:" URIs to support abstract unix domain sockets. (#24500)
    Increment Index when parsing not plumbed SAN fields. (#24601)
    Revert "Revert "Deprecate GRPC_ARG_HTTP2_MIN_SENT_PING_INTERVAL_WITHOUT_DATA_MS"". (#24518)
    xds: Set status code to INVALID_ARGUMENT when NACKing. (#24516)
    Include stddef.h in address_sorting.h. (#24514)
    xds: Add support for case_sensitive option in RouteMatch. (#24381)
    Removing TLS workaround for Android NDK r12b. (#24283)

C++

    Fix --define=grpc_no_xds=true builds. (#24503)
    Experimental support and tests for CreateCustomInsecureChannelWithInterceptorsFromFd. (#24362)

(wiz)