Fixes to Console and Variables keybindings

[lionel-]

These fixes depend on each other so I gathered them in a single PR. Each commit can be cleanly reviewed separately though. Happy to split in multiple PRs if that would be preferred.

Fix shadowing of user keybindings

Addresses #2857.

The first commit improves the detection of extra modifiers in our keydown handlers for Console and Variables viewpanes. This allows unrelated commands to dispatch correctly, e.g. our Cmd+C handler will not prevent a user keybinding Shift+Cmd+C from running.

QA notes: The keys handled in these locations should still work as expected:

• positron/src/vs/workbench/contrib/positronConsole/browser/components/consoleInstance.tsx

  Line 342 in 2062523

  const keyDownHandler = async (e: KeyboardEvent<HTMLDivElement>) => {

• positron/src/vs/workbench/contrib/positronConsole/browser/components/activityPrompt.tsx

  Line 69 in 2062523

  const keyDownHandler = async (e: KeyboardEvent<HTMLDivElement>) => {

• positron/src/vs/workbench/contrib/positronVariables/browser/components/variablesInstance.tsx

  Line 152 in 2062523

  const keyDownHandler = async (e: KeyboardEvent<HTMLDivElement>) => {

In particular, typing text when the console is scrolled up should scroll all the way to the bottom, there should not be some pixels left to scroll.

Some of the keybindings such as for Copy, Cut, Paste, and Select all differ depending on the platform. MacOs uses the Cmd prefix key whereas other platforms use Ctrl.

Fix keybindings in foreign keyboard layouts

Addresses #2724.

The second commit changes our handlers to use the key field of keyboard events instead of code fields. The former represents the character typed according to the user's keyboard layout. The latter represents the physical location on the keyboard, which doesn't match the layout.

Restore cut command in console

Addresses #2549.

Third commit removes a registered keybinding for Cmd/Ctrl+X that was bound to an empty command. It was added in #1118, I assume to pair it with the context menu action for Cut. However removing it does not affect the context menu. And it turns out that the default Cut implementation pretty much does what we want:

• It's disabled when the selection is read-only or overlaps with a read-only section.
• It's enabled when the selection is writable, as in our input code editor.

Add paste handler to readline prompts

Addresses #2863.

Fourth commit implements select-all and paste in readline prompts. Paste is a quick stopgap implementation on top of the <input> HTML element. The direct HTML manipulation confuses undo/redo. I think we'd be better off using a VS Code code text editor that accepts text edits so that undo/redo work out of the box.

[jmcphers]

LGTM, and was able to verify these fixes with a locally built copy of the branch! Feels nice.

[jmcphers]

Seems fine as a stopgap, but it is not clear to me why we need to reimplement paste here -- shouldn't we get that for free as part of the HTML input control?

[lionel-]

I was wondering too, given that Copy and Cut are working as expected. Perhaps relatedly, the onPaste= handler is not run if I pass one to the <input> element. VS Code's keyboard troubleshooter does not react to the event so it's not some dispatch that takes over.