vscode: Support location in TerminalOptions

[xai]

What it does

Support location in TerminalOptions, whereas location can be

• a TerminalLocation enum with the values Editor and Panel
• a TerminalEditorLocationOptions object which contains a ViewColumn and an optional preserveFocus boolean
  ViewColumn can be Active, Besides, or an explicit column from One to Nine
• a TerminalSplitLocationOptions object which contains a parentTerminal that is supposed to be split.

Contributed on behalf of STMicroelectronics

Fixes eclipse-theia#11506

How to test

• Download test extension and copy it into the plugins folder.
• Start Theia and verify that the commands provided by the test extension trigger the correct¹ behavior:
  • Open terminal in editor opens a terminal in the main area
  • Open terminal in panel opens a terminal in the bottom area
  • Open terminal with TerminalSplitLocationOptions splits the provided parent terminal, the test extension uses the most recent one as parent argument
    Apparently, this one is currently broken in VS Code and just opens a terminal/tab in the panel area without splitting anything
  • Open terminal with TerminalEditorLocationOptions provides quick picks for ViewColumn and PreserveFocus
    • ViewColumn 'Active' should open terminal in the current column
      Apparently this is currently broken in VS Code, it seems to always open a tab in the first column. No idea what is actually supposed to happen - maybe tab in active column if there already is a terminal?
    • ViewColumn 'Besides' should open a terminal to the right of the current terminal
    • ViewColumn should open a terminal in the specified column if possible
    • PerserveFocus specifies whether the focus should remain untouched (default is false)

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

Footnotes

1. The VSCode API specification and the current behavior of VSCode seems to be misaligned and at least partly broken in VSCode. ↩

[lucas-koehler]

I had a look at the code and have some minor remarks/questions. I will test this beginning of next week.

[lucas-koehler]

I tested the changes with the provided extension and it worked well for me.

I added one more minor inline suggestion.