Use immutable arrays inside our special codegen events.

Add test around roundtripping parameters symbols for VB events.

VBCSCompiler currently requests a GC during "quiet time" (when the compiler hasn't received a new build request for 30s), but it doesn't do an LOH compaction or do multiple GCs to pump through finalizers. This PR does both of these things, resulting in significantly more memory being released during the quiet time.

SymbolDisplayVisitor.CreateAliasMap – pop out of speculative semantic model to lookup for declared aliases.

Load IOptionPersisters in RoslynPackage

Update nuspecs for netstandard1.3 change

Be resilient to not being able to get a SymbolTreeInfo for a given PEReference

Implements support for type characters in tuple types in VB.

Support round-tripping of anonymous functoins and anonymous delegates.