Support template literals

[vgrichina]

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_literals

Regular template literals would be very nice for stuff like logging, so that you can basically have stuff like:

log(`transaction: ${hash} status: ${status}`);

instead of current

log('transaction: ' + hash.toString() + ' status: ' + status.toString());

This looks like a feature which only requires compiler-level sugar and zero runtime support.

More than that, we probably can hijack tagged templated literals to support UTF-8 string literals, i.e. have stuff like:

let utf8String = u`Hello, World`;

[mdaj06]

@dcodeIO can i have a look at it?

[vgrichina]

@mdaj06 BTW this issue is something we are interested to give grant for:
https://gov.near.org/t/assemblyscript-grant-q1-2021/697/3

[mdaj06]

sure got it!

[MaxGraey]

Template literals mostly finished: #1715

[dcodeIO]

Initial support for template literals has been merged now, with tagged template literals not enabled just yet due to having to account for an edge case first, which requires implementing ReadonlyArray.