Fix #24817 - Prevent overflow of the message in define keybinding widget.

Treat emmet snippets as textmate

./features/implementationProvider or ./features/ImplementationProvider ?

Queuing a large number of WinJS promises that aren't actually async can lead to a stack overflow. Also this is faster.

Fixes #24688

Fixes #24630
Related #19665

Fixes #24898

Fixes #24808

**bug**
Markdown preview updates when you zoom. The root cause is that previews are updated whenever the config is changed.

**Fix**
Extract preview config to its own well defined object. Only update the preview when the keys we care about in the config change