feat(dts-generator): huge update to the currently used generator

This updates the dts-generator in this repository from the vastly outdated version from years ago to the one developed and used internally over the past years in the build-up to officially releasing production-ready type definitions for UI5. The new dts-generator is based on the old version developed here, but has undergone huge changes and extensions.

Changes to the dts-generator package itself include:

Conversion of the implementation to TypeScript
Creation of type definitions declaring ES modules instead of globals (globals still supported as alternative output, though)
Completely new API
Loads of adaptations to generate better type definitions, partly depending on changes in the UI5 codebase, so this new version might not run with older versions of UI5 like 1.90 or even before
MUCH more... in general you are better off considering this a new project, although at the core of it quite some parts of the old implementation and overall structure are still there

Other changes to the repository include:

Upgrade TypeScript and Prettier and sync the versions across the repository
Update other dependencies like husky
Update documentation to the new reality
Update test code to work with the new dts-generator API
Update test content/snapshots
Delete all demos, as they are outdated (using types with globals)

Changes to the ts-interface-generator are NOT done in this commit to not cause a major version increase. Those changes are basically just dependency updates and handled in a separate commit. This may mean that both commits should be regarded as parts of ONE change and may not work without each other (as e.g. both affect yarn.lock, but this file is only touched in this commit).

BREAKING CHANGE: the API and behavior and generation results of the dts-generator have completely changed. To migrate, basically re-write the usage of it.

SAP / ui5-typescript

feat(dts-generator): huge update to the currently used generator #436