feat(terminal): synchronize onOutput with buffer updates using onWriteParsed

[Fangoling]

What it does

This implements the feature proposed in #16874.

Previously, the onOutput event fired immediately when write() or writeln() was called. This change buffers the output data and defers the event emission until xterm fires onWriteParsed.

This prevents race conditions by ensuring the onOutput event fires only after xterm has fully parsed and synchronized the buffer, rather than immediately upon the method call.

How to test

1. Start theia with the flag --log-level=debug
2. Type anything in the terminal
3. Check in the browser console that the state of the terminal buffer that is logged is the same as the current terminal buffer
4. Check in the browser console that the payload of the event equals your input

Follow-ups

Breaking changes

• This PR introduces breaking changes and requires careful review. If yes, the breaking changes section in the changelog has been updated.

Attribution

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[ndoschek]

Hi @Fangoling, could you add a few test instructions in the PR description please? TIA!

[Fangoling]

Hi @Fangoling, could you add a few test instructions in the PR description please? TIA!

I added two logs on debug level to the event for testing purposes of this pr. I would remove them before the merge of this pr.