Test Encoder.Convert and UTF8Encoder.Convert behaviors.
Added class ExposedEncoder to test the virtual method Encoder.Convert behavior.
Test UTF8Encoder.Convert override.
Add test for Regex.Match with anchors on a substring.
Regex fixes for substring parsing.
Add test for Regex RTL substring matching.
Added classes EncodingEncoder and EncodingDecoder.
EncodingEncoder and EncodingDecoder override Encoder.Convert.
The Convert overrides allow retrieval of chars/bytes buffers with the same size as .NET.
[ms.build] Do not try to release threads upon finalization.
[ms.build] Fix bug #20961 - add KeepDuplicates etc. to 4.0 as internal.

Since NET_4_0 and NET_4_5 share the same ToolsVersion (4.0) there seems no
way to distinguish the appropriate framework .targets file, so I ended up
to add the missing members as internal for 4.0.
[ms.build] add some cyclic dependency related tests (some are not working).
[mcs] auto-property initializer can be array initializer
[mcs] Any type parameter is allowed for null propagating operator
[mcs] nameof operator
[corlib] Remove heavyweight EndsWith from 1bff9d890f95e72e4145d48980a05908c87b53ce
[System.Net.Http] Handle quoted filename value. Fixes #21960
Re-enable valid tests
[runtime] Fix logic when allocating code region if the first try at a fixed address fails.
[System] Implemented .NET 4.5 overloads for GZipStream and DeflateStream.

Fixes xambug #21982.
[System] Restrict GZip/DeflateStream tests to .NET 4.5.
[delegate-virtual-trampoline] Add virtual parameter to existing JIT time code path
[delegate-virtual-trampoline] Add virtual functions delegate trampoline support

This optimization is activated in the ldvirtftn + delegate case, and is deactivated in the case where the architecture does not support it (mono_arch_get_delegate_virtual_invoke_impl return NULL)
[arm64] Allow v8..v15 in unwind info on arm64. Fixes part of #21615.