Deno: Rewrite Deno.readFile and Deno.writeFile to use more primitive ops

[ry]

Should be a simple fix - perhaps using Buffer for readFile.

Sync versions should be done too.

At the end the readFile and writeFile ops should be removed completely from cli/msg.fbs

[bartlomieju]

I'm working on it

[bartlomieju]

@ry just so we're on the same page, we want to rework readFile and writeFile to use shared queue rather than old way with flatbuffers?

[ry]

@bartlomieju No - implement them as a series of read and write ops. This should be a pure TS patch.

open/read/write/close