Strictify on all layers

[turt2live]

Why?

The non-strict aspects of TypeScript allow for a lot of flexibility but also make it easy for errors to slip in, e.g. when there is no strong contract on null-ness.

What?

We’ll fix all existing strict-mode violations and enable all strict-mode checks to run on PRs. This will allow us to eliminate entire classes of errors through static code analysis.

Reference: https://www.typescriptlang.org/tsconfig#strict

Plan

### matrix-js-sdk
- [x] Enable `strict` in matrix-js-sdk

### matrix-react-sdk
- [x] Enable `noImplicitThis` in matrix-react-sdk
- [x] Enable `strictBindCallApply` in matrix-react-sdk
- [x] Enable `alwaysStrict` in matrix-react-sdk
- [ ] https://github.com/vector-im/element-web/issues/21968
- [ ] https://github.com/vector-im/element-web/issues/21967
- [x] Enable `strictFunctionTypes` in matrix-react-sdk
- [x] Enable `strictPropertyInitialization` in matrix-react-sdk
- [x] Enable `useUnknownInCatchVariables` in matrix-react-sdk
- [x] Enable `noUnusedLocals` in matrix-react-sdk
- [x] Enable `strict` in matrix-react-sdk

### element-web
- [x] Enable `noImplicitThis` in element-web
- [x] Enable `strictBindCallApply` in element-web
- [x] Enable `alwaysStrict` in element-web
- [x] Enable `noImplicitAny` in element-web
- [x] Enable `strictNullChecks` in element-web
- [x] Enable `strictFunctionTypes` in element-web
- [x] Enable `strictPropertyInitialization` in element-web
- [x] Enable `useUnknownInCatchVariables` in element-web
- [x] Enable `noUnusedLocals` in element-web
- [x] Enable `strict` in element-web

### element-desktop
- [x] Enable `strict` in element-desktop

[Johennes]

@t3chguy did a quick pulse-check of what's left in matrix-react-sdk right now:

Strict attribute	Errors	Files
useUnknownInCatchVariables	151	64
strictFunctionTypes	102	57
strictNullChecks	4749	699
strictPropertyInitialization	167	~20

Note that strictPropertyInitialization cannot be enabled until strictNullChecks is enabled.

We also have some statistics on https://arewetsyet.bit.ovh/ but they're currently broken.

[t3chguy]

noImplicitAny cannot be enabled until strictNullChecks either in our case due to some of the js-sdk relying on the strict parser for implicit typing

[t3chguy]

I am making good progress with strictNullChecks - down to 2645 errors in 400 files