TypeScript/JavaScript docs improvements (#5984)

* use correct language formatter for TypeScript examples

* fixes typo in JS/TS copied from PHP (apparently)

the variables are not named with a prefixed `$`

* fixes bizarre line breaks in markdown examples

* fixes snake case typo to fit JS/TS conventions

* makes example of Uint8Array usage explicit

* removes random extra lines between language blocks

* adds simple example for writing to file in node

* typo: flabuffers => flatbuffers

* adds (previously missing) code blocks to TypeScript code block

* adds context about where `monster_generated` comes from

to the uninitiated, a bit of help like this is welcome