Migrate from `vscode-nls`/`vscode-nls-dev` to `vscode-l10n`

[Colengms]

The underlying libraries that facilitate string localization in VS Code extensions (vscode-nls/vscode-nls-dev) have been replaced with a new library: vscode-l10n.

https://github.com/microsoft/vscode-nls
https://github.com/microsoft/vscode-nls-dev
https://github.com/microsoft/vscode-l10n

Opening this issue to track migrating to the new library.

[sean-mcmanus]

The current vscode-nls appears to be causing the performance issue at #14549, which is about a 1 second synchronous block of CPU processing on startup, which supposedly would be fixed by switching to vscode.l10n / @vscode/l10n.