Add parallel front end robustness test to ui tests #139312

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10 errors and 1 warning

expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found reserved keyword `virtual`

feature has been removed

expected value, found trait `Sized`

cannot find value `i` in this scope

expected trait, found builtin type `i32`

expected trait, found function `generator_capture`

yield syntax is experimental

`impl Trait` is not allowed in cast expression types

yield syntax is experimental

the feature `generic_const_exprs` is incomplete and may not be safe to use and/or cause compiler crashes