debt - no guessing-caching, better use of gc-signals, command converter using gc-signals, main side heap service

* a declared module allows to have a sibling module containing experimental API
* this change also cleans up some bogous type pollution that happened because vscode used to be both, a declare module and a global namespace

let plugin host commands internally also accept ICommandHandlerDescriptions and have a way to get them all

# Conflicts:
#	src/vs/languages/html/common/htmlTags.ts

first steps in exposing language featues as command. done with: hover, definition, workspace symbols