Implement C++ API for defining channel filters.

Fix the ThreadPoolExecutor: max_workers can't be 0 in _channel_connectivity_test and _channel_ready_future_test

Hopefully fixing #7639.

Splitting out interop's server helper.

Manual upmerge after version bump.

Add a RecordingThreadPool that inherits from Executor, contains a
ThreadPoolExecutor and has an extra method 'was_used' to indicate if
submit method was ever called i.e. if the thread pool was ever used.

Conflicts:
	CMakeLists.txt
	Makefile
	build.yaml
	package.json
	src/core/lib/surface/version.c
	src/csharp/Grpc.Auth/project.json
	src/csharp/Grpc.Core/VersionInfo.cs
	src/csharp/Grpc.Core/project.json
	src/csharp/Grpc.HealthCheck/project.json
	src/csharp/build_packages.bat
	src/node/health_check/package.json
	src/node/tools/package.json
	src/python/grpcio/grpc_version.py
	src/python/grpcio_health_checking/grpc_version.py
	src/python/grpcio_tests/grpc_version.py
	src/ruby/lib/grpc/version.rb
	src/ruby/tools/version.rb
	tools/distrib/python/grpcio_tools/grpc_version.py
	tools/doxygen/Doxyfile.c++
	tools/doxygen/Doxyfile.c++.internal
	tools/doxygen/Doxyfile.core
	tools/doxygen/Doxyfile.core.internal

Fixing json parsing issues detected by libfuzz.

Let override default response size limit

deflake grpclb_test

Fix Objective-C test pods for Cronet tests

Move timeout_encoding to core/lib/transport

Stop using image aliases, as this is getting deprecated.

Backport of "added windows to INSTALL.md"

added windows to INSTALL.md

added windows to INSTALL.md