Add new context keys of 4K builds to the keymap schema.

[UltraInstinct05]

This PR adds newly added context keys of the 4K build series to the keymap schema.

Note: These aren't in the official documentation yet. There is an open issue for it sublimehq/sublime_text#4063

Notes:

1. I haven't added is_javadoc because I don't know what it does as a context key. I have marked the description for it as a TODO in PackageDev.

2. panel_type is a new one (not yet added to PackageDev), added in 4097. (Will do so in a future PR to it)

[rwols]

I'm wondering where these context keys are described? I can't find them on docs.sublimetext.io nor on https://www.sublimetext.com/docs/key_bindings.html#context

EDIT: I guess the linked issue is enough proof :)

[UltraInstinct05]

I'm wondering where these context keys are described? I can't find them on docs.sublimetext.io nor on https://www.sublimetext.com/docs/key_bindings.html#context

As I said, it's not yet in the official documentation. One has to go through the Default/Default ($platform).sublime-keymap to find these. As for the community docs, there is an open issue to add these sublimetext-io/docs.sublimetext.io#39