Adds support for TypeScript 4.8 and resolves some issues that came up as a result of the update.
Most of the issues came from some changes in TypeScript where the `decorators` and `modifiers` properties were removed from most node types, and were combined into a single `modifiers` array. Since we need to continue supporting TS 4.6 and 4.7 until v15, I ended up creating a new `ngtsc/ts_compatibility` directory to make it easier to reuse the new backwards-compatible code.
PR Close#47038
