Consider reading sources even when some types cannot load

[nohwnd]

Due to library mismatch, some types might fail to load from the assembly when PortableReader is used. This ends up throwing TypeLoadException, and skipping the whole source lookup. Which means no tests in the assembly will have source information.

This exception can be swallowed and the types that were loaded from the assembly can be read from the exception properties, which should allow us to return the data we were able to gather without skipping the others.

See this PR for the description of the problem, a piece of code in static method loaded roslyn types, and those failed to load an older version of System.Collections.Immutable.

dotnet/fsharp#16545 (review)