merge editor - caller reverts

[bpasero]

This PR fixes #

[bpasero]

A new consequence of this change is the following error when selecting "Do not save":

ERR Model is disposed!: Error: Model is disposed!
    at TextModel._assertNotDisposed (vscode-file://vscode-app/Users/bpasero/Development/Microsoft/vscode/out/vs/editor/common/model/textModel.js:243:23)
    at TextModel.getLineMaxColumn (vscode-file://vscode-app/Users/bpasero/Development/Microsoft/vscode/out/vs/editor/common/model/textModel.js:571:18)
    at isAtEndOfLine (vscode-file://vscode-app/Users/bpasero/Development/Microsoft/vscode/out/vs/workbench/contrib/mergeEditor/browser/model/diffComputer.js:102:32)
    at normalizeRangeMapping (vscode-file://vscode-app/Users/bpasero/Development/Microsoft/vscode/out/vs/workbench/contrib/mergeEditor/browser/model/diffComputer.js:72:43)
    at rangeMappingFromCharChange (vscode-file://vscode-app/Users/bpasero/Development/Microsoft/vscode/out/vs/workbench/contrib/mergeEditor/browser/model/diffComputer.js:64:16)
    at vscode-file://vscode-app/Users/bpasero/Development/Microsoft/vscode/out/vs/workbench/contrib/mergeEditor/browser/model/diffComputer.js:54:59
    at Array.map (<anonymous>)
    at fromLineChange (vscode-file://vscode-app/Users/bpasero/Development/Microsoft/vscode/out/vs/workbench/contrib/mergeEditor/browser/model/diffComputer.js:54:50)
    at vscode-file://vscode-app/Users/bpasero/Development/Microsoft/vscode/out/vs/workbench/contrib/mergeEditor/browser/model/diffComputer.js:30:46
    at Array.map (<anonymous>)
    at Function.fromDiffComputationResult (vscode-file://vscode-app/Users/bpasero/Development/Microsoft/vscode/out/vs/workbench/contrib/mergeEditor/browser/model/diffComputer.js:30:35)
    at EditorWorkerServiceDiffComputer.computeDiff (vscode-file://vscode-app/Users/bpasero/Development/Microsoft/vscode/out/vs/workbench/contrib/mergeEditor/browser/model/diffComputer.js:27:61)
    at async TextModelDiffs.update (vscode-file://vscode-app/Users/bpasero/Development/Microsoft/vscode/out/vs/workbench/contrib/mergeEditor/browser/model/textModelDiffs.js:42:28)

[jrieken]

@bpasero can you clarify? will the workbench revert the changes? The goal is that with "auto save: off" and users selecting "don't save" everything is undone to their state on disk

[bpasero]

@jrieken yeah we revert here based on the result of confirm:

vscode/src/vs/workbench/browser/parts/editor/editorGroupView.ts

Lines 1606 to 1607 in d6a9b52

	// first try a normal revert where the contents of the editor are restored
	await editor.revert(this.id);