write callback support

[jerch]

PR for callback support in write methods. Also simplifies the write interface supporting both string and raw UTF8 bytes (Uint8Array) in one method.

With the changes its possible to get notified once a chunk of data was parsed by xterm.js:

• with string data

...
await new Promise(resolve => term.write('some string data', resolve));
doSomething(); // executed after the chunk was processed
...

• with utf8 bytes

...
await new Promise(resolve => term.write(new Uint8Array([66, 67, 68]), resolve));
doSomething(); // executed after the chunk was processed
...

Fixes #2408.

[jerch]

@Tyriar Was worried that merging the input types along with the additional callback handling would create a negative perf impact, but thats not the case:

   Context "out-test/benchmark/test/benchmark/Terminal.benchmark.js"
      Context "Terminal: ls -lR /usr/lib"
         Context "write"
            Case "#1" : 5 runs - average throughput: 29.05 MB/s
         Context "writeUtf8"
            Case "#1" : 5 runs - average throughput: 35.94 MB/s

Thats on par with our current separated handling without any callback stuff. Same results in the demo with ls -lR /usr - no significant difference.

[Tyriar]

Looks good so far, still a todo list to action before merging

[Tyriar]

@jerch is this ready for review/merge?

[jerch]

@Tyriar Yepp I think so, well - might need some polishing.

[Tyriar]

lgtm, nice work! 👍

[Tyriar]

🎉

microsoft/vscode@c2e7944