Avoid lowering timeoutlen when running in VS Code, to avoid
unwanted timeouts from key mappings.
The lower value of 300ms (down from Neovim's default of 1000ms)
works great outside of VS Code, where it helps trigger the which-key UI
quickly, and where which-key prevents timeouts from occuring.
But in VS Code (where which-key isn't applicable), the lower value
makes it difficult to perform some key mappings in time,
such as `]p`, which requires shifting hand position.
29ed06e000