vscode: Support isTransient in TerminalOptions and ExtensionTerminalOptions

[lucas-koehler]

What it does

• Extend TerminalOptions and ExtensionTerminalOptions with isTransient property according to the VSCode API
• Add terminal preference enablePersistentSessions with default value true
• Adhere to pref. enablePersistentSessions and option isTransient in the terminal widget

Fix #11777

Contributed on behalf of STMicroelectronics.

Signed-off-by: Lucas Koehler [email protected]

How to test

1. Get example extension from here or package it from source
2. Open command palette and execute Terminal API: Create Transient Terminal
3. Open a second regular terminal
4. Reload the page. After the reload, the transient terminal should be gone while the regular one is reloaded
5. Open settings and search for Enable Persistent Sessions. Disable the setting
6. Repeat steps 2 and 3
7. Reload the page. After this reload, both terminals should be gone
8. Reset the setting.

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

[vince-fugnitto]

LGTM 👍 I confirmed that:

• the example plugin works well when the preference is on/off
• terminals are not persisted when created outside the VS Code API