The assertThrows and assertDoesNotThrow methods expect either a
function to execute, or a string to eval. In several tests however we
accidentally passed the *result* of the statement to be tested instead
of the code.
This CL adds check to catch such error early, and removes wrong uses.
In most places, we do not need to use assertDoesNotThrow anyway,
because exceptions are handled as test failures.

Drive-by: Unify catch syntax in mjsunit.js and make sure to propagate
MjsUnitAssertionErrors correctly.

R=mathias@chromium.org

Bug: v8:8562
Change-Id: I88894a667cbe0570774f748a9a23e8a527887a49
Reviewed-on: https://chromium-review.googlesource.com/c/1439238Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59277}