Set vim.command in VSCodeContext on key press.

[raineorshine]

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What this PR does / why we need it:

This PR sets vim.command in VSCodeContext to recordedState.commandString. This allows pending actions that are waiting for a movement argument (e.g. d or y) to be read in the when clause of keyboard shortcuts.

There is currently no change to VSCodeContext in such a pending state, making it impossible to correctly configure some keyboard shortcuts, such as commands that should be activated in Normal mode, but not if a command is started. Making that information available in VS Code's context gives users greater flexibility and precision in setting up custom keyboard shortcuts.

Which issue(s) this PR fixes

Fixes #7833 by allowing users to add !vim.command to the when clause of the keyboard shortcut.

Special notes for your reviewer:

I didn't see a good way to add a unit test for this, as I am not sure how to access VSCodeContext within a test, but I did build and debug the change with Inspect context keys and confirm that vim.command gets updated as the user types and properly reset when their command completes.

[Guray00]

awesome idea, I'm still waiting for this feature.

[leftbones]

Also waiting for this feature. I use Shift+H and Shift+L to move between editors in Vim, but in VSCodeVim if I try to use rH or rL to single replace, it moves editors instead. Not a problem in Vim itself.