Const provides better type guards and can make logic clearer

We compile using the alwaysStrict flag so these directives are not needed

This part removes most `use strict` directives that are right after the file header

There are many places in the code that do `import Event, { ...} from '.../event'`.

Rename to make it more clear that these APIs are for `vscode.TextEditor`

This reverts commit 4a3dbb6c.

This reverts commit 7cb8ac43.

Have `workspace.applyEdit` correctly account for model version changes and reply with false if a model was loaded and changed in the meantime

* fix spelling of 'iff' and 'idenifier'

* Keep 'iff' in comment if it means *if and only if*

* 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