"Rename Symbol" operations combine with the previous undo step

[benblank]

When editing a JavaScript file (I haven't tested with other file types), renaming multiple symbols in a row, then attempting to undo the last one, will result in all of them being undone.

• VSCode Version: Code 1.14.0 (b8cd5b9, 2017-07-10T18:24:22.120Z)
• OS Version: Darwin x64 16.6.0
• Extensions:

Extension	Author (truncated)	Version
vscode-eslint	dba	1.2.11
gitlens	eam	4.3.1
vscode-ember	emb	0.1.0
vsc-ember-cli	fel	0.3.3
csstriggers	kis	0.3.1
cpptools	ms-	0.12.0
vscode-icons	rob	7.10.1

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Steps to Reproduce:

1. Open a new file (Cmd-N).
2. Change the language mode to JavaScript (Cmd-Shift-P, "mode", Enter, "javas", Enter).
3. Type const foo = 1; and press Enter.
4. Type const bar = 2; and press Enter.
5. Ctrl-click on the token "foo", select "Rename Symbol", type "foo1", and press Enter.
6. Ctrl-click on the token "bar", select "Rename Symbol", type "bar2", and press Enter.
7. Undo a single step (Cmd-Z).
8. Observe that both rename operations have been undone.

Reproduces without extensions: Yes

[mjbvz]

This does not seem JavaScript specific. @alexandrudima or @rebornix Can you please take a look since this involves the undo history

[alexdima]

@jrieken undo stops can be pushed via model.pushStackElement

two calls should be made, before and after the call to model.pushEditOperations in
https://github.com/Microsoft/vscode/blob/7494a1b944e9a81c504a0a6f1bc33f5522cd81cc/src/vs/editor/common/services/bulkEdit.ts#L117