putty-style ED2 sequence handling as terminal option

[Blashaq]

This PR is related to the problem discussed in #1727.

goals:

• Allow xterm.js based applications to change CSI 2 J sequence behaviour to non-canon, which is sometimes preferred by users.
• Keep canon handling of CSI 2 J (clear whole screen) as default.
• Alternative handling will push erased text to the scrollback and trim empty lines. This is the way PuTTY and some other terminals do it by default.

changes made:

• New configuration option: scrollOnDisplayErase in ITerminalOptions.
• InputHandler.eraseInDisplay will behave differently if this option is set.
• Added some tests.

[jerch]

Thx for looking into this.

Beside the minor code suggestion below - LGTM 👍

[Blashaq]

Thanks for suggestions, this is indeed cleaner (and also works, to no suprise ).

[jerch]

@Blashaq The CI tests dont run yet, seems scrollOnDisplayErase is missing in src/common/services/Services.ts in ITerminalOptions?

[Blashaq]

You're right, sorry. I have accidentally skipped that file in my commit.

[jerch]

There are still linter some issues.

[Blashaq]

Everything should be fine now 🙏

[jerch]

@Blashaq LGTM 👍, works like a charm, many thx for the PR.

@Tyriar There seems to be an issue with clear under with linux with ED3 - the new scrollbar gets not updated by ED3 yet. Maybe this not enough to announce the changes:

xterm.js/src/common/InputHandler.ts

Line 1238 in 41e8ae3

this._onScroll.fire(0);

Imho its not linked to this PR, thus I create a new ticket. --> #5228