Deduplicate InMemoryTextResource

[gbodeen]

What it does

Fixes #9191 and an unreported issue with Search-In-Workspace: when clicking a search-and-replace suggestion, the preview editor should reveal the line on which the suggested change occurs. Currently on master, only the first suggested change in a file will be revealed.

(Please let me know if these should be separate PRs or instead should be flattened into a single commit. I found the latter issue while testing the fix for issue 9191, and it was unsatisfying to submit a fix that still looked broken.)

How to test

Test Bulk-Edit:

1. Open ts/tsx file, click a function name and press F2 to rename it.
2. Enter new name and press Shift+Enter.
3. A Refactor Preview pane should open in bottom with suggested changes.
4. Click on one of the changes suggested in that pane.
5. A split preview editor should open displaying the diff. This preview uses a mem-txt scheme.

Test Search-In-Workspace:

1. Use the search-in-workspace widget. Click the Toggle Replace triangle and enter replacement text.
2. Click one of the suggested search-and-replace operations.
3. A split preview editor should open displaying the diff. This preview uses a 'mem-txt' scheme.
4. Additionally, the preview editor should now reveal the line of the suggested change.

Review checklist

• as an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• as a reviewer, I agree to behave in accordance with the review guidelines

[vince-fugnitto]

The changes work well for me 👍

• confirmed that rename preview works as on master.
• confirmed that search-in-workspace rename works.
• confirmed that search-in-workspace rename now properly selects the proposed changes.

[gbodeen]

Incidentally, I noticed that this fixes another cosmetic issue: In the search-and-replace tree, an element will now stay selected after clicking it. This happens because the mode: 'reveal' option is now passed to the editor in all cases.