DEC Locator mode

### Description of the new feature

Basically the 30 year older and more powerful alternative to #18591 to handle some mouse cursor stuff for SIXEL applications.
(Creating this issue now cause it might get closed due to #19949.)

Some discussion on why to support this including GIF showcase: https://github.com/microsoft/terminal/issues/18591#issuecomment-2671611361 (and following comments).

SGR is not _that_ widely used and if only SGR was supported it would obviously increase the amount of applications that could instead use Locator mode if it was supported.
If Locator mode was supported in such a widely used terminal emulator, a case could be made for other terminal emulators not that widely spread to support it as well, increasing general terminal-ecosystem feature-parity with older VTs.

### Proposed technical implementation details

_No response_

Read the discussion linked from #18591 first, then check #19949 to determine whether this request is superseded. No files or tests are named, and the proposed technical implementation is empty; done would require an agreed scope and working DEC Locator mode support for SIXEL applications.

Written by the indexing model from the issue text.