Performance issues/timeouts on some grammars

[tomtau]

Possibly related issues:

• oss-fuzz: timout in parser #675
• This grammar kills the online editor #603
• [BUG] Pest.rs hangs indefinitely with this grammar #571
• Timeout in recursion #402
• Very slow parsing of certain grammars #279

Suggestions from @dragostis :

Ideally, the optimizer should be able to detect all exponential cases and have replacement rules for them. Maybe someone could take a look at egg and implement a simplified version of the grammar there so peephole optimizations can be more easily written?

plus more context on why packrat parsing wasn't used: #684 (comment)