JS: Fix jump steps generated by IIFEs and exception flow

[asgerf]

This PR fixes a few issues that cause performance (and precision) problems:

• Removes jump steps generated by local flow into and out of immediately-invoked function expressions (IIFEs), and fixes some bugs so that the same flow is now handled by regular flow rules. IIFEs are special-cased in the local flow relation, which benefits things like type tracking and type inference, but is unhelpful for the data flow library.
• Removes jump steps resulting from exception-propagating flow steps. A flow summary is now used to propagate exceptions out of callbacks. Apart from the added precision of not using jump steps, the new version also errs on the side of propagating exception more often, using a denylist rather than an allowlist to specify functions that propagate exceptions from callbacks.
• js/insecure-randomness now blocks flow through test cases. Perhaps more queries ought to do this, but it seems particularly problematic for this query. Also broadens our classifications of test files a bit.

Evaluation of d1c9e47 looks good:

• Yet another 78% speedup on vscode, which means it is down to being "only" 79% slower than on main (the similar numbers is a coincidence).
• 48 fixed FPs, mainly due to the change to js/insecure-randomness
• 2 gained FPs, due to imprecise higher-order function flow combined with more exception propagation.

Evaluation of d1c9e47 against main shows that we're down to a median 26% slowdown, with a 100% worst-case slowdown.

Evaluation of ce00bd2 vs d1c9e47 is underway