fix: support osx shortcuts

Description

This MR provides support for osx shortcut keys by dispatching keydown events from the iframe to the vscode window as well as supporting the following incoming events:

• copy
• paste
• cut
• selectstart / selectall

Related Issues

Issue Commands input and other keystrokes are not wor... (gitlab-org/editor-extensions/gitlab-lsp#380 - closed) • John Slaughter • 17.5

How has this been tested?

What CHANGELOG entry will this MR create?

• fix: Bug fix fixes - a user-facing issue in production - included in changelog
• feature: New feature - a user-facing change which adds functionality - included in changelog
• BREAKING CHANGE: (fix or feature that would cause existing functionality to change) - should bump major version, mentioned in the changelog
• None - other non-user-facing changes