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.
[jit] Fix enum->int casts in gsharedvt code. Fixes #21893.
[mcs] null propagating operator and extension methods
[runtime] Fix Process.PrivateMemorySize64 etc. on ios. Fixes #21882.
[mcs] null propagating operator and expressions which cannot be null
[System] Disable failing test
[sdb] Avoid asserting when a cattr cannot be loaded. Fixes #21653.
[jit] Avoid taking the loader lock in mono_jit_compile_method_inner (), it shouldn't be needed any more.
[jit] Reorganize the locking in mono_jit_compile_method_inner, the domain lock already makes the code lookup+insert atomic, no need to do more work inside the jit code hash lock. Also lock jit_code_hash in mono_jit_free_method ().
adding the mutex header file dependency
Implemented System.IO.Compression.FileSystem.
Merge pull request #1196 from tritao/master

System.IO.Compression.FileSystem implementation
Fixed Path.GetFullPath to work correctly when the current path is '/'.

Fixes xambug #833.
Merge pull request #1201 from crisdut/fix-win-mono-dependencies

Adding the mutex header file dependency
Merge pull request #1190 from esdrubal/encoder-convert

System.Text.Encoder convert
[ms.build] Do not try to release threads upon finalization.