Get rid of getRootSymbol and include target's flags in transient symbol'...

...s flags

We had three functions:
* getRootSymbol
* getRootSymbols
* getTargetSymbol

I worked with @sheetalkamat to do a few things. We got rid of getRootSymbol. Also, for every symbol that has a target, we copy the flags from the target. There are also several changes in the ScriptElementKind logic in services.ts, which are not quite finished.