Rewrite Buffer.BlockCopy in C# (dotnet/coreclr#27216)
Rewrite Buffer.BlockCopy in C# (dotnet/coreclr#27216)

* Rewrite Buffer.BlockCopy in C#

Fixes #27106

* Workaround to enable type check optimizations for BlockCopy only

Signed-off-by: dotnet-bot <03c4cb6107ae99956a7681f2c97ff7104809a2bd@microsoft.com>

ericstj/corefx,shimingsg/corefx,shimingsg/corefx,ericstj/corefx,ericstj/corefx,shimingsg/corefx,ericstj/corefx,ericstj/corefx,shimingsg/corefx,ericstj/corefx,shimingsg/corefx,ericstj/corefx,shimingsg/corefx,shimingsg/corefx