chore: simplify generator

[Lodin]

This PR significantly simplifies React wrapper generation; instead of TypeScript AST, it uses plain strings which improves the readability of the code. The code has been reduced by more than half as well. TypeScript is still used for catching syntax errors and apply common style in generated files; though, we can remove this step if needed.

Also, the generator script drops the custom fswalk and fromAsync functions in favor of the native glob (it is experimental but since it is our internal script I consider it ok). However, this change requires Node v22 LTS.

Since there are two packages managed by a root tsconfig, and glob needs newer TS libs, I had to switch the root to esnext. To keep packages on es2021, I created separate tsconfig.json files for each package. So, now, we can use es2021 for packages and use any modern stuff in our scripts.

EDIT:
Since I faced an issue in vaadin/hilla repo (we use Node v20 instead of Node v22 for building Vaadin 24.x, and going to move to Node v22 only in Vaadin 25), I decided to replace the native glob with the similar implementation from the node-glob package. I have also replaced all the obsolete utils (fswalk and fromAsync) with the glob, which revealed a minor error in the package.json update (deeply nested CSS folders were not visited and put into the package.json).

[sissbruecker]

Some TeamCity agents still run Node 18, which means that building the project would not work there. See also #311.

Let's see that agents are updated first before merging this.