Draft: Switch to `ts-for-gir` (take 2)

This supersedes !118, and allows us to switch to typescript types generated by ts-for-gir instead of (the now unmaintained) gi.ts

• It currently uses https://github.com/vixalien/gi-typescript-definitions for type definitions
• The type definitions are generated by ts-for-gir
• Simplifies the typescript setup

However, there are some outstanding issues that need to be fixed on the ts-for-gir before we can utilise their generated types. You can find most of them in their issue tracker, but here are the ones that are currently blocking this:

• https://github.com/gjsify/ts-for-gir/issues/222
• https://github.com/gjsify/ts-for-gir/issues/221
• https://github.com/gjsify/ts-for-gir/issues/220

cc @JumpLink P.S. thanks so much!!