add baseline for linked editing

[iisaduan]

The baseline lets us know exactly when linked editing does and doesn't occur, and it makes long tests more readable.

[andrewbranch]

Didn't look too closely at the baseline generation but the result looks great!

[DanielRosenwasser]

Mostly looks good, though there's some duplication and style nits to address

[DanielRosenwasser]

Suggested change

	const n = inlineLinkedEditBaseline[inlineLinkedEditBaseline.length - 1];
	baselineContent += `[|/*${n.index}*/` + fileText.slice(n.start, n.end) + `|]` + fileText.slice(inlineLinkedEditBaseline[inlineLinkedEditBaseline.length - 1].end) + linkedEditInfoBaseline;
	const lastRange = inlineLinkedEditBaseline[inlineLinkedEditBaseline.length - 1];
	baselineContent += `[|/*${lastRange.index}*/` + fileText.slice(lastRange.start, lastRange.end) + `|]` + fileText.slice(lastRange.end) + linkedEditInfoBaseline;

[DanielRosenwasser]

Actually, maybe instead of copying the same contents within the loop, you just loop on every element and then write

const sliceEnd = i + 1 < inlineLinkedEditBaseline.length ?
    inlineLinkedEditBaseline[i + 1].start :
    undefined;
const trailingText = fileText.slice(e.end, sliceEnd);

baselineContent += `[|/*${e.index}*/` + fileText.slice(e.start, e.end) + `|]` + sliceEnd;

[DanielRosenwasser]

Is there any reason that this is named index if it's always initialized with the current offset? Maybe offsetForBaseline or something?

[DanielRosenwasser]

Also, since it's an array

Suggested change

	let inlineLinkedEditBaseline: { start: number, end: number, index: number }[] = [];
	let inlineLinkedEditBaselines: { start: number, end: number, index: number }[] = [];

[iisaduan]

index is the number it will be labeled with in the baseline output, and it's initalized to offset since it made sense to me to just use the variable that's passed into the function. offset is incremented per list entry in linkedEditsByRange like an index.

[DanielRosenwasser]

@typescript-bot cherry-pick this to release-5.1

[typescript-bot]

Heya @DanielRosenwasser, I've started to run the task to cherry-pick this into release-5.1 on this PR at 8a8956a. You can monitor the build here.

[typescript-bot]

Hey @DanielRosenwasser, I've opened #54419 for you.

[sheetalkamat]

I think you can skip mentioning ranges here since they are already marked in the text above.