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.

Previously, when parsing a local function we held off on creating the
node until we actually saw a body because the local function could be
ambiguous with an await statement until then. However, we never verified
that the parsed return type was "await", meaning we were overly
conservative in classifying incomplete local functions. This created a
very bad typing experience where completion could not tell that you were
declaring a local function until the body, which created many incorrect
results in the completion list, including in the generic parameter list.

This change verifies that the return type we've parsed is actually the
literal text "await" before considering the parse ambiguous.

Fixes #13480.

Cache what symbols a serialized defintion rehydrated to.  

Cache what symbols a serialized defintion rehydrated to.  That way we don't have to recompute it every time we hear about a new reference.

FindReferences: Do not cascade to anonymous *delegate* parameters.

Update SymbolKey to use the new CreateAnonymousType api.

wait for finalizers to release all garbage at the end of the build

Remove hashcodes from symbol keys.