JavaScript in the fancy-regex syntax set never finishes on a two-line input #166

With two-face 0.5.2+bat-0.26.1 (syntect-fancy) and syntect 5.3.0, the syntax named
JavaScript in the fancy set does not return from ParseState::parse_line on this input:

  | { type: "a" }
  /** x */

The second line runs for minutes at flat memory. An onig-linked syntect build, with the
syntax selected by name, hangs the same way, so the cause is in the definition, not in the
regex engine.

Cause: expression-statement-continuation matches empty (the / of /* is in its operator
class), and the "rest of the line is blanks and comments" rule also matches empty; the two
set each other forever. syntect's loop guard only catches non-consuming pushes
(trishume/syntect#706 diagnoses this; #460 is the older report).

sublimehq/Packages fixed the definition in #3257 (2022-11), but that fix uses branch_point,
which syntect 5.3.0 cannot load. bat avoids the hang by mapping js to JavaScript (Babel),
which the fancy set excludes. So a fancy-set user who resolves js by token gets the
looping definition.

Possible ways out, your call: note it in the README's fancy-set legend, or ship a patched
JavaScript in the fancy set that drops the empty match.

Found in mdmost (https://github.com/oetiker/mdmost), which now guards against it with a
per-line token limit in a vendored syntect.