exhaustive quickcheck syntax fails formatting with ParseError

[mikex-oss]

Describe the bug
The new feature implementing #1715 by PR #1829 seems to work as a DSLX test, but the formatter errors out with:

Formatting failed: Error: INVALID_ARGUMENT: ParseError: 
Expected '=', got ')'
=== Source Location Trace: ===
xls/dslx/frontend/bindings.h:58
xls/dslx/frontend/token_parser.cc:102
xls/dslx/frontend/parser.cc:1714
xls/dslx/frontend/parser.cc:391
xls/dslx/parse_and_typecheck.cc:71
xls/dslx/dslx_fmt.cc:91

To Reproduce
The new example in the documentation triggers this behavior:

// `u8` space is small enough to check exhaustively.
#[quickcheck(exhaustive)]
fn prop_double_bitreverse(x: u8) -> bool {
  x == rev(rev(x))
}

Expected behavior
Formatting succeeds.

[mikex-oss]

@cdleary for vis

[cdleary]

@mikex-oss thanks, we should probably also check the documentation examples auto-format in addition to running them as tests -- I should be able to fix quickly

[cdleary]

@mikex-oss note in #1832 I could not observe this via unit tests, your dslx_fmt may be stale?

[mikex-oss]

Sorry for the noise. I forgot (again) about the delay due to the release cadence of our autoformatter, so these types of changes aren't available atomically.

Confirmed this is working now.