Add grammar performance warning

[Yanpas]

Inspired by microsoft/vscode#92369

[Yanpas]

This code is executed in the browser context, so there is no need in perf_hooks module

[alexdima]

@Yanpas
Thank you for your PR. But:

1. This node module needs to execute in browsers and in nodejs, so we cannot use perf_hooks.
2. We cannot just console.warn with a somewhat random time limit. VS Code ships to millions of devices with different specifications, and such a performance problem should be investigated by the grammar author, and no cycles should be spent to record duration on end users machines. In other words, IMHO, it is not useful to run this troubleshooting code all the time.

That being said, perhaps the Registry or the tokenize call can get some kind of option called "profile: true" or something. Then, only if that option is set, the times will be recorded. Then, we can adopt this in VS Code and check if running from source and then enable that flag.

[Yanpas]

1. I can use smth like (performance as any)?.now(). (Sadly this is not merged perf_hooks: expose performance global nodejs/node#28635)
2. I think we can reuse DebugFlags.InDebugMode. It is enabled easily via VSCODE_TEXTMATE_DEBUG env.

[alexdima]

• DebugFlags.InDebugMode makes sense.
• Date.now() can be used everywhere.

[Yanpas]

Date.now() is unsuitable cause it's not monotonic. (You called Date.now, OS scheduler stopped the process, some other process did it's work (language server e.g.), now our process has CPU again and consecutive call Date.now will return all time that has passed in real life, not process's life.

So I see no other option as proposed above

[Yanpas]

Updated branch

[alexdima]

Thank you!