✨ Add "Clear To Start" (⌘K) shortcut to integrated terminal

### Is your feature request related to a problem? Please describe.

_No response_

### Describe the solution you'd like

Pressing ⌘K while focused on the integrated terminal should clear the terminal window and the scrollback buffer.

### Describe alternatives you've considered

Could potentially be an option that can be enabled/disabled, but see below for why it should be enabled by default.

### Additional context

The ⌘K shortcut is pretty standard across macOS terminals (see Terminal.app, Hyper, VS Code integrated terminal, etc). ⌘K functions similar to the Ctrl-L shortcut or `clear` command, but additionally clears the scroll backbuffer.