feat: add alert, confirm, and prompt

[kt3k]

This PR adds alert, confirm, and prompt functions from web standards.

You can write simple interaction script like the below with this change.

const name = prompt('What is your name?');
console.log(`Hello ${name}!`);

$ ./target/debug/deno run test.ts
What is your name? John
Hello John!

Maybe these features are not so important for advanced users, but I think these could be very helpful for beginners of Deno or learners of the language.

---

closes #4257

[nayeemrmn]

When not interactive, we should do what browsers do when dialog boxes are disabled.

[nayeemrmn]

LGTM

[kryptish]

I like this, anything speaking against merging this? =)

[bartlomieju]

@kt3k this looks great! I love how simple the implementation is and having this API enables users to create simple CLI scripts without additional libraries. Please the branch so we can land it

[kt3k]

@bartlomieju Thank you for the feedbacks! Rebased the branch! I'll add the handling (and tests) of yes, Yes, etc in confirm function a little later. Keep it as is for now.

[bartlomieju]

LGTM, great feature @kt3k!

[bartlomieju]

Yikes, it looks like @kitsonk had a lot of concerns for this API in #4257. @kitsonk are you still against them? If so, I will do the revert.

[David-Else]

These are awesome. I hope to teach kids programming and see Deno as a perfect way to provide everything they will need in one executable. I can even teach typed vs untyped going from JS to TS, these kinds of simple API's to do essential things are so important. It is the difference between friendly and easy to understand vs annoying and pointless time-wasting.

[Bestulo]

Is there any way to use these as promise instead of blocking?

edit: guess it could be a child process that reads from console but that sounds over the top

[Soremwar]

@Bestulo Alert, confirm and prompt are all abstractions over a simple stdin/stdout program, it's quite easy to implement asynchronously without this API