#1835 subtly changed the semantics of the `LoadFile` plugin hook to no
longer have the current script location available for signature files
being loaded through `@load-sigs`. This was undocumented behavior, so
it's technically not a regression, but since at least one external
plugin is depending on it, this change restores the old behavior.
The new hooks works similar to the existing `HookLoadFile` but,
additionally, allows the plugin to return a string that contains the
code to be used for the file being loaded. If the plugin does so, the
content of any actual file on disk will be ignored (in fact, there
doesn't even need to be a file on disk in that case). This works for
both Zeek scripts and signatures.
There's a new test that covers the new functionality, testing loading
both scripts and signatures from memory. I also manually tested that the
debugger integration works, but I don't see much of a way to add a
regression test for that part.
We keep the existing hook as well for backwards compatibility. We could
decide to deprecate it, but not sure that buys us much, so left that
out.
Closes#1757.
