Modify protected async functions to use try/with
ProjectFactory invalidates FCS before it removes ProjectProvider from its cache
remove an obsolete open declaration
remove all event listeners from VSLanguageService

ProjectFactory calls VSLanguageService.InvalidateProject only on onProjectItemChanged
Merge pull request #498 from vasily-kirichenko/fix-misbehaviour-on-added-files

ProjectFactory invalidates FCS before it removes ProjectProvider from its cache
Remove unnecessary try/with block
Merge pull request #497 from dungpa/safe-async

Modify protected async functions to use try/with
graying unused declarations
SourceCodeClassifier peeks meaningful categories, then Other, then Unused if there are many for one symbol
fix the order in which SourceCodeClassifier peeks categories