10357: internal: fix and force-disable block validation ;-( r=matklad a=matklad Originally we tried to maintain the invariant that `{}` always match. That is, that in the parse tree the pair of corresponding `{}` is always first and last tokens of some nodes. We had the code to validate that, but apparently it's been broken for **years** since we introduced tokens/nodes split. Fixing it now makes some tests fail. It's unclear if we want to keep this invariant: there's a strong motivation for breaking it in the following case: ``` use std::{ // unclosed paren fn main() { } } // don't actually want to pair up this with the one from `use` ``` So let's fix the code, but disable it for the time being bors r+ 🤖 Co-authored-by: Aleksey Kladov <[email protected]>