Cleanup for comments from pull request #3439, switch to tern hinting

This is fixes for the minor issues discussed in https://github.com/adobe/brackets/pull/3439

Update jsdoc
use ExtensionUtils.getModulePath instead of manually slicing up path
use FileUtils.readAsText instead of DocumentManager when we only need the text on disk
Call CollectionUtils.hasProperty instead of Object.prototype.hasOwnProperty...
Add comment explaining logic around finding location of called function for function type hinting
remove unnecessary calls to setCursorPos
remove stale comments in unittests
pull out hint invalidation check into a function and remove check for query.length === 0, not necessary anymore