Get rid of `curly_block` method

[matklad]

We have a curly_block method over here: https://github.com/matklad/libsyntax2/blob/357cd3358167daa38f3ff34d225e1501faff6015/src/parser/event_parser/parser.rs#L179.

This is a high-order function which eats a balanced paren sequence inside of {}, which helps quite a lot with error recovery, because all errors are contained in a block. However, this high order function does not help much, and I suggest just removing it and writing while loops by hand, like in here:

https://github.com/matklad/libsyntax2/blob/357cd3358167daa38f3ff34d225e1501faff6015/src/parser/event_parser/grammar/items.rs#L108-L114

Ideally, the error block should handle { specially (by parsing a balanced sequence), like it is done in Kotlin:
https://github.com/JetBrains/kotlin/blob/4d951de616b20feca92f3e9cc9679b2de9e65195/compiler/frontend/src/org/jetbrains/kotlin/parsing/KotlinParsing.java#L438