Merge #7513
7513: NFA parser for mbe matcher r=matklad a=edwin0cheng
Almost straight porting from rustc one, but a little bit slow :(
```
rust-analyzer analysis-stats -q .
```
From:
```log
Database loaded: 636.11ms, 277minstr
crates: 36, mods: 594, decls: 11527, fns: 9017
Item Collection: 10.99s, 60ginstr
exprs: 249618, ??ty: 2699 (1%), ?ty: 2101 (0%), !ty: 932
Inference: 28.94s, 123ginstr
Total: 39.93s, 184ginstr
```
To:
```log
Database loaded: 630.90ms, 277minstr
crates: 36, mods: 594, decls: 11528, fns: 9018
Item Collection: 13.70s, 77ginstr
exprs: 249482, ??ty: 2699 (1%), ?ty: 2101 (0%), !ty: 932
Inference: 30.27s, 133ginstr
Total: 43.97s, 211ginstr
```
Fixes #4777
Co-authored-by: Edwin Cheng <edwin0cheng@gmail.com>
91bf5fa827