Convert to typescript

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Discussed during quarterly planning last week, every developer is to take on converting a sim to typescript to take the new language for a test drive. Since this sim is my next sim I'm going to be working on (for voicing), I will start here, and with https://github.com/phetsims/chipper/blob/master/doc/typescript-quick-start.md. My expectation is that it will take one day (8 hours).

Note phetsims/tasks#1096

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Big work that I'm putting off right now:

• adding types out stateObject outputs, for example, NumberIO returns a number, but sometimes a string too.

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I started with about 1350 compiler errors when converting all resources to *.ts. After completing the model, I'm down to 1100, and with strict mode off, its 888. I'm going to commit to a branch to start.

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After the above commits, I am down to 500 compile errors.

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So far, I have found ~3 actual bugs (boolean passed in for number, or null for number, etc), and about 5-10 cleanup pieces, like extra parameters passed in that were ignored.

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Branch merged, lint and ts compile errors have been either fixed or worked around.

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There are still a fair number of usage of merge that I kept around because the supertype isn't in typescript yet. I thought that was easiest. I also got rid of a bunch of ts-ignore usages. All that are left are from old-style mixins.

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010ffb4 was a documentation and general Typescript review. I haven't updated options, ts-ignores, TODOs or anys just yet.

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Ok, I have done all the optionize that I can do at this time. I'll wait for more common code to be converted.

Other TODOs will be discussed during this week's dev meeting.

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Ok! I got rid of many TODOs here, still some remain as common code is not yet in typescript yet (SoundClip, SoundGenerator, ScreenIcon, KeyboardHelpSection).

• 8 usages of any
• 2 ts-ignore
• 9 TODOs to this issue.
• I should still go through and mark all members readonly that should be marked as such. Perhaps there is a lint rule for that. (Ahha! https://typescript-eslint.io/rules/prefer-readonly/)

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A couple more TODOs taken care of here since SoundClip and SoundGenerator are now typescript.

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The only thing left for this issue is to convert KeyboardHelpSection code to typescript once those common code types are complete.

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New convention to adopt: initialize in the declaration site when possible.

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New convention to adopt: initialize in the declaration site when possible.

I went through all files. Closing!