[System.Configuration/Test] Try to track down failure in buildbot

This TestConnectionStringRetrieval unit test (committed by me some months
ago) succeeds for me in a clean checkout, but I don't understand why it
fails in the buildbot, so let's place some sanity check in it.
Merge pull request #808 from knocte/master

[System.Configuration/Test] Try to track down failure in buildbot
[ilasm] Fixes forwarded types namespace encoding
[mcs] Missing type forwarded types should not cause type collision. Fixes #16196
[mcs] Assignment to value type readonly generated variables needs to check all member access expressions. Fixes #15832
[runtime]When setting a loader error, clear the previous one to avoid the leak.
[runtime]Type parsing of generics should not rely on the presence of a backtick. Fixes #15124.

We previously depended on the presence of a backtick in a generic type name to try to
parse a generics argument list. This is not what the spec says and F# breaks this expectation.

The right way to handle this is to probe for array syntax.
Add some tests for #15124.
[aot] Increase a buffer size to avoid an assert. Fixes #16239.
[Mono.Debugger.Soft] Added FlagsAttrbite where appropriate
[sdb] Add an ExitCode property to VMDeathEvent. Fixes #16113.
[jit] Make the exceptions.cs test suite runnable in mobile.