fix: Remove invasive split terminal action

[rschnekenbu]

What it does

Partially removes some intrusive split terminal actions in views

Current situtation:

fix #12357

Contributed on behalf of STMicroelectronics

How to test

To test in theia:

• Check that by default, split terminal action does not appear on toolbars for various views.
• Check that on terminal views, the split terminal icon is still present when the terminal view is active
• terminal context menu still displays the split terminal entry

Limitations: when a terminal is active, there are still some polluting split terminal entries on some views.

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

[tsmaeder]

@rschnekenbu since I don't have write access to the branch, you'll have to rebase on master, @rschnekenbu

[tsmaeder]

@rschnekenbu and now the signed-off-by header, please.

[tsmaeder]

Sorry, it's not the signature, seems to be a problem with the dependencies.

[tsmaeder]

@rschnekenbu now the PR needs another lift to master. If you "allow edits by maintainers" on the PR, I could just push the button.

[tsmaeder]

Looks good to me and test OK for me.