Improve performance of hidden node parsing

[msujew]

I've noticed in a project with a large file with a lot of comments (~20 000 LoC, ~10 000 comments), that parsing started taking a huge performance hit. It seems like our current method of iterating through the CST to add hidden nodes leads to super-linear behavior in the parsing phase.

You can reproduce this by using the test I've added to langium-parser.test.ts and run it on the current main branch. While the parse takes only ~150ms on my machine with the new changes, it takes roughly ~5000ms on main.

This change replaces the existing hidden node placement algorithm with a different one that should perform linearly. Note that the placement of the hidden nodes has not changed with this algorithm. Existing tests (and also a few new ones) verify this behavior.

Some ideas for this new algorithm were taken from #1733.

[Lotes]

I was hesitating with the approval, but actually there is no need for waiting, I got it. If you want an additional approval or more comments, you could reach out for Ben. Or ask me, what I should look at specifically.