bumped debugger-libs for iOS debugger fix
Updated references to xwt, md-addins
[Ide] Add new PlatformService.OpenTerminal variant

It supports setting the window title and environment variables.
[Core] Add explanatory comment for a hack
[Windows] Implement PlatformService.OpenTerminal
[MSBuild] Builder interface library doesn't need to be an x86 exe

Make it an AnyCPU library to fix warnings and prevent executing it.

Assembly identity is still the same.
[MSBuild] Add assembly redirects to v12 builder
[MSBuild] Reorganize the builders' assembly redirects
Fixed 'Bug 17277 - Code analysis having problems with corelib'.
[Ide] GetCacheDirectory has now a more fine grained locking strategy &
only touches the cache on first access.
[Core] Fix all the warnings
[Core] Fix TargetFramework race

If something tried to request an unknown TargetFramework during
TargetRuntime initialization, then the framework collection could
be altered while being accessed.
Revert "Fixed 'Bug 17277 - Code analysis having problems with corelib'."

This reverts commit ed8032b1d1c97fd9b057338a53a33fc6e299d8c3.
This commit broke several code completion related tests and turned the
build orange.
Revert "Revert "Fixed 'Bug 17277 - Code analysis having problems with corelib'.""

This reverts commit f3b05bf63e6af89e19f6f65252d57920da48f7cd.
[Ide] Fixed unit tests