add support for selectionRange command

[ananthakumaran]

TypeScript 3.5 added selectionRange command which provides functionality similar to https://github.com/magnars/expand-region.el

[josteink]

I saw this too in the TS3.5 announcement and was conflicted about creating an issue for it or not.

Looking at the expand-region code though, it seems to provide mode-specific implementations for each major mode it supports.

While tide is a minor-mode, wouldn't the correct thing to do, be for us to provide a tide-mode implementation for expand-region, instead of doing our own thing?

The way I see it now:

1. we create a defun for tide-expand-region.
2. we create a PR for expand-region to use this function when tide-mode is active.
3. existing expand-region users won't need to setup any new or typescript-mode specific keybindings for this functionality.

Any opinions? Sounds good?

[MarcusRiemer]

I am not quite sure whether I really like the way selectionRange behaves and I love the way tide allows me to do things "on demand" instead of hijacking default actions. So properly boundling this with a mode sounds like the way to go for me.