Async task timings

[dktapps]

Introduction

This PR adds support for asynchronously collecting timings, and for collecting timings from AsyncWorkers for AsyncTasks.

The implemented API allows custom collect callbacks to be registered, which allows plugins to include custom thread timings in timings reports. This is necessary because other threads' timings records can't be directly accessed from the main thread.

Relevant issues

Closes #6166

Changes

API changes

• TimingsHandler::printTimings() is now deprecated
• Added getToggleCallbacks(), getResetCallbacks() and getCollectCallbacks() to TimingsHandler

Behavioural changes

• Timings reports now include AsyncTask timings.
• Timings may now take slightly longer to generate as the report generator has to wait for other threads to respond.
• Timings report version 3 is now used. This tells the timings viewer to use the ThreadId part of timer group names to namespace timer IDs (necessary since timer IDs could otherwise collide between different threads).

Backwards compatibility

Should be fully backwards compatible

Follow-up

Requires translations:

Name	Value in eng.ini
N/A	Compiling timings report

Tests

I tested this PR by doing the following (tick all that apply):

• Writing PHPUnit tests (commit these in the tests/phpunit folder)
• Playtesting using a Minecraft client (provide screenshots or a video)
• Writing a test plugin (provide the code and sample output)
• Testing via command and pasting reports

Samples

This requires a version of the timings viewer including the following commit: pmmp/timings@13cefa6

An example report can be viewed here: https://timings.pmmp.io/?id=330357

[dktapps]

There are some unrelated changes in the PR which I made to facilitate this feature, such as Promise::all() supporting 0 promises. These should be separated before merging.