Add support for touchscreen selection

[moetayuko]

Description of the new feature/enhancement

I'm a Surface pro user and sometimes need to use CLI tools without bothering to pick up the keyboard (although it's a mess to type with on-screen keyboard), but it turns out that Windows Terminal is not optimized for touchscreen at all.

Proposed technical implementation details (optional)

As far as I can tell, the following need to be implemented:

1. Automatically popup on-screen keyboard and resize the window to fit it on touch.
2. Long press to select/copy/paste.
3. Zoom with finger gestures (Touch Zoom with two fingers don't work on Touch screen (but it works on Touch Pad) #3149)

[Nyameliaaaa]

Not Useful For Developers

[DHowett-MSFT]

@diligamer do you speak for all developers?

[Nyameliaaaa]

@DHowett-MSFT Well, Most Developers Don't Use Touchscreens.

[zadjii-msft]

@diligamer Ah yes, but some developers do use touchscreens, so we shouldn't discount the opinion of a minority of users based solely on the fact that they're a minority.

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Back on topic, I could have sworn that @leonMSFT actually already implemented having the on-screen keyboard appear when you tap on the Terminal. @dianlujitao what verison of the Terminal are you using?

I'm fine with leaving this open to track "Long press to select/copy/paste.", since

• "Automatically popup on-screen keyboard and resize the window to fit it on touch." should already work
• "Zoom with finger gestures" is already being tracked by Touch Zoom with two fingers don't work on Touch screen (but it works on Touch Pad) #3149.