Links get re-evaluated when buffer changes happen outside viewport

[Tyriar]

Repro:

1. Run ls to fill viewport
2. Open vscode repo in terminal
3. Echo a url
4. Run ./scripts/test
5. Scroll up while that's running and hover the url, the underline will flicker

---

The issue is confusion between requesting re-rendering of dirty rows relative to ybase:

xterm.js/src/common/InputHandler.ts

Lines 498 to 499 in 1618092

	// Refresh any dirty rows accumulated as part of parsing
	this._onRequestRefreshRows.fire(this._dirtyRowTracker.start, this._dirtyRowTracker.end);

Then incorrectly firing onRenderedViewportChange incorrectly even when the viewport isn't re-rendered when scrolled up:

xterm.js/src/browser/services/RenderService.ts

Lines 169 to 171 in 1618092

	if (!this._isNextRenderRedrawOnly) {
	this._onRenderedViewportChange.fire({ start, end });
	}

And assuming that the event is relative to ydisp:

xterm.js/src/browser/Linkifier2.ts

Lines 323 to 331 in 1618092

	this._linkCacheDisposables.push(this._renderService.onRenderedViewportChange(e => {
	// Sanity check, this shouldn't happen in practice as this listener would be disposed
	if (!this._currentLink) {
	return;
	}
	// When start is 0 a scroll most likely occurred, make sure links above the fold also get
	// cleared.
	const start = e.start === 0 ? 0 : e.start + 1 + this._bufferService.buffer.ydisp;
	const end = this._bufferService.buffer.ydisp + 1 + e.end;

[jerch]

@Tyriar Wow, nice find. Could this also be the reason for the selection events being fired over and over while input flows, although there is no active selection?

[tisilent]

Links in tests.....

[tisilent]

20230920_091001.mp4

Flashing like this.

[Tyriar]

There seems to be a bigger problem here where we often render when nothing happens just from input that was written below. Terminal.refresh is called for the viewport (relative to ydisp), but often (not always) the intent is to refresh the bottom viewport only.

[Tyriar]

@tisilent that's probably some Windows-only wrapping/reflow issue.

[Tyriar]

@jerch yeah probably. Do we have an issue tracking that?