Don't send mouse reports with non-finite coordinates

[MocA-Love]

Drop mouse reports whose coordinates are NaN or infinite, instead of sending them to the pty.

Fixes #6108

Related: microsoft/vscode#328696

Problem

With mouse reporting on, xterm.js can send reports with NaN coordinates:

• SGR: the report contains the text NaN, e.g. \x1b[<0;NaN;NaNm.
• DEFAULT: the report contains NUL bytes, because String.fromCharCode(NaN) is \0.

There are two known paths:

1. The terminal element is removed from the DOM while a mouse button is held. The mouseup listener is still on document. getComputedStyle on the detached element returns an empty padding, and parseInt('') is NaN. This is the ^[[<0;NaN;NaNm in Terminal sends \x1b[<0;NaN;NaNm to the pty when a file link is activated by ctrl+click microsoft/vscode#328696.
2. Inertia scrolling dispatches an event without clientX (_inertia in src/browser/scrollable/touch.ts), as described in Inertial fling sends NaN mouse coordinates when mouse reporting is on #6108.

Cause

• src/browser/input/Mouse.ts:6-15: getCoordsRelativeToElement subtracts parseInt(padding) and uses clientX as is. Either one can make the result NaN.
• src/browser/services/MouseCoordsService.ts:33-46: getMouseReportCoords clamps with Math.min / Math.max. Both return NaN for NaN.
• src/browser/services/MouseService.ts:497-502: the range check e.col < 0 || e.col >= cols || ... is false for NaN, so the event passes. The encoders in src/common/services/MouseStateService.ts:125-150 then build the report.

Fix

1. getMouseReportCoords returns undefined when the element-relative coordinates are not finite. Both callers (_sendEvent and _handleTouchScrollAsWheel) already stop on !pos.
2. _triggerMouseEvent also rejects non-finite values, so other callers are covered too:
   • The col/row check is now !(e.col >= 0 && e.col < cols && e.row >= 0 && e.row < rows), which fails for NaN.
   • x and y (used by SGR_PIXELS) have no range check, so they must be finite.

How this relates to #6059

#6059 takes option 1 in #6108: it stops touch.ts from creating an inertia event without clientX. This PR takes options 2 and 3: the reporting path rejects bad coordinates, whatever the source. It also covers the detached-element path, which #6059 does not touch. This PR does not change touch.ts, so the two PRs do not conflict and can land in any order.

Testing

• New tests:
  • MouseService _triggerMouseEvent > non-finite coords: NaN or ±Infinity in col, row, x or y sends no report, with the DEFAULT, SGR and SGR_PIXELS encodings.
  • MouseCoordsService.test.ts (new file): an event without clientX / clientY, or with NaN / Infinity, returns undefined. A normal event still returns the cell and pixel coordinates.
• The 4 new failure-case tests fail without the fix and pass with it.
• jsdom returns "0" for the padding of a detached element, so the unit tests cover the detached case through the missing-clientX path, not through an empty padding.
• npm run test-unit: 2408 passing. npm run lint: passes.
• I did not run the Playwright integration tests, and I did not reproduce the bug in a browser.

Repro (not verified in a browser)

1. Open the demo and write \x1b[?1000;1002;1006h to the terminal (button-event tracking, SGR encoding).
2. Press a mouse button in the terminal and keep it held.
3. In the devtools console, run term.element.remove().
4. Release the button.

Expected before: the data handler receives \x1b[<0;NaN;NaNm. Expected after: no report.

Notes

• In the detached-element case, the button release is now not reported at all. The application does not get a release for that press. This is the same as the existing behavior when the char size is not valid: getMouseReportCoords already returns undefined there, and no report is sent.