Don't rescan doc for html instrumentation when reattaching to editor

[redmunds]

This is for #9303

Rescanning doc blows away old ids and replaces them, so synchronization is lost.

This was broken with fix for #7886, so verify that is still fixed.

[JeffryBooher]

I'm seeing this when switching panes:

Uncaught TypeError: Cannot call method 'getSelections' of null HTMLDocument.js:189

This breaks live editing

[JeffryBooher]

1. Open citrus completed
2. Split view vertical
3. Open index.html in right pane (not sure if it matters but that's how i reproduce it)
4. Start live editing
5. edit some stuff on the page like you would for smoke tests
6. click in the left pane (it should be empty)
7. click in the right pane
   ==> RTE
   the RTE may happen at step 6

[JeffryBooher]

Also I did this a few more times and got this:

Document ref count has fallen below zero! ErrorNotification.js:117
Couldn't find the dom for C:/Users/jsbooher/Documents/GitHub/brackets/test/smokes/citrus completed/index.html ErrorNotification.js:117
Couldn't find the dom for C:/Users/jsbooher/Documents/GitHub/brackets/test/smokes/citrus completed/index.html ErrorNotification.js:117

[redmunds]

@JeffryBooher Great catch! This also happens in master, so it doesn't seem to be related to this change. Let's track that in a separate issue.

[redmunds]

We should re-test every feature with Split View! :)

[JeffryBooher]

Looks good to me... merging.