Allow loading of extraperfect files from all root dirs

[lgoettgens]

The former code for loading perf27.grp and perf33.grp tried to load them using READ_GAP_ROOT which only checks the root directories in SyGapRootPaths aka the root paths that are known at GAP's startup e.g. via the -l flag.
However, this won't check any root directories that were added later using ExtendRootDirectories.

This PR changes this to check all root directories in GAPInfo.RootPaths. The motivation for this is in OSCAR, where we want the julia lazy artifact handler to do the downloading of these files on first access, but due to how julia loads OSCAR and GAP.jl, this seems to be only possible using ExtendRootDirectories. (x-ref oscar-system/Oscar.jl#4592)

cc @fingolfin @ThomasBreuer

[fingolfin]

@ThomasBreuer any objections to merging this?

[ThomasBreuer]

I think that this proposal is fine for the moment.

As soon as READ_GAP_ROOT, ReadGapRoot, ReadLib, ReadGrp have access to the full list of root directories, we could change the code again, in order to call ReadGrp in both places in question.

[fingolfin]

Indeed, but that work will only be in GAP 4.15, while this patch can be backported for 4.14.1 :-)