Merge in 'release/5.0' changes

Skip some PKCS9 tests on NetFx (dotnet#45213)

Skip some PKCS9 tests on NetFx (dotnet#45213)

[release/5.0] [browser][crypto] Remove restraining not supported attr…

…ibute Primitives (dotnet#43441)

Co-authored-by: Kenneth Pouncey <kjpou@pt.lu>

[release/5.0] [browser][crypto] Remove restraining not supported attr…

…ibute Primitives (dotnet#43441)

Co-authored-by: Kenneth Pouncey <kjpou@pt.lu>

Fix System.Net.Sockets telemetry (dotnet#42726)

Leftover Utf8String defines are causing ILLinker warnings (dotnet#41680)

The CreateRuntimeRootILLinkDescriptorFile task, which generates most of S.P.CoreLib's ILLink.Descriptor file for coreclr, doesn't respect #ifdefs. So even though FEATURE_UTF8STRING is disabled in the release/5.0 branch, it is still generating entries for Char8 and Utf8String. But since these managed types do not exist, the ILLinker is raising warnings.

To fix this, comment the DEFINE_CLASS entries out of the header file.

Fix dotnet#41654

Minimum CMake downgrade for Linux (dotnet#39044) (dotnet#40471)

Co-authored-by: Santiago Fernandez Madero <safern@microsoft.com>
Co-authored-by: Jan Vorlicek <janvorli@microsoft.com>

Co-authored-by: Jeremy Koritzinsky <jekoritz@microsoft.com>
Co-authored-by: Santiago Fernandez Madero <safern@microsoft.com>
Co-authored-by: Jan Vorlicek <janvorli@microsoft.com>

[release/5.0-preview7] Disallow unrestricted polymorphic deserializat…

…ion in DataSet (dotnet#39314)

Fixes CVE-2020-1147
https://portal.msrc.microsoft.com/en-us/security-guidance/advisory/CVE-2020-1147
See also https://go.microsoft.com/fwlink/?linkid=2132227.

SafeProcessHandle.Unix: fix missing DangerousRelease (dotnet#37412) (d…

…otnet#37446)

Because the SafeProcessHandle was not owned, ReleaseHandle was
not called, causing the wrapped SafeWaitHandle to never release
its resources.

Co-authored-by: Tom Deseyn <tom.deseyn@gmail.com>