Use multi-chord shortcuts to match Emacs

I haven't tested this, but based on the README:

Commands working with types (marked with the 🎚 emoji below) can have different levels of normalization. However, due to some technical limitations, we cannot prefix commands with C-u or C-u C-u like in Emacs. Instead, we replace the C-u C-c prefix with C-u and the C-u C-u C-c prefix with C-y.

The technical limitations part refers to the upstream issue in VSCode, which I believe has been implemented: https://github.com/microsoft/vscode/pull/175253.

If so, the default shortcuts need to be changed to match Emacs because that's the current go-to editor for Agda, which many users will be familiar with. Emacs shortcuts are also something you can see often in third-party documentation or tutorials, just because it's the default. By having the same set of shortcuts, it'll make it easier for current Emacs users to transition to this extension.

As an aside, I personally prefer more ergonomic shortcuts, like in Spacemacs, but that can always be configured by the users. This can be also provided in settings, in addition to the default Emacs shortcuts.

I think there's also value in keeping the current shortcuts as is because they are more ergonomic than the default Emacs ones. So this could be a setting in the configuration:

emacs (multi-chord)
spacemacs (with spc) - this one might be also useful for the Vim extension users, like myself (due to conflicting shortcuts in the current default)
vscode (current).

banacorn / agda-mode-vscode

Use multi-chord shortcuts to match Emacs #181