Implement List(iter,func)

[fingolfin]

@mohamed-barakat asked for it during the last GAP Days in September 2018, and now again @markuspf, so I polished up the code I wrote for @mohamed-barakat back then and added some tests.

[codecov]

Codecov Report

Merging #2960 into master will decrease coverage by 8.74%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2960      +/-   ##
==========================================
- Coverage   83.79%   75.05%   -8.75%     
==========================================
  Files         682      624      -58     
  Lines      346236   311983   -34253     
==========================================
- Hits       290135   234162   -55973     
- Misses      56101    77821   +21720

Impacted Files	Coverage Δ
lib/coll.gi	95.62% <100%> (-0.77%)	⬇️
lib/contfrac.gi	6.66% <0%> (-83.34%)	⬇️
lib/proto.gi	2.04% <0%> (-81.64%)	⬇️
lib/ctbllatt.gi	0.88% <0%> (-79.93%)	⬇️
lib/ctblauto.gi	6.15% <0%> (-77.9%)	⬇️
lib/teachm2.g	23.07% <0%> (-76.93%)	⬇️
lib/algliess.gi	0.99% <0%> (-74.51%)	⬇️
lib/ctblpope.gi	1.82% <0%> (-72.35%)	⬇️
src/modules.h	33.33% <0%> (-66.67%)	⬇️
lib/attr.gi	33.33% <0%> (-66.67%)	⬇️
... and 383 more

[markuspf]

Looks good to me.

The only nitpick I have is that I think there's no documentation for this (which is a.. "more general problem").

[fingolfin]

Also, I guess one could expect to have this also for Filtered, Number, ForAll, ForAny, Product, Sum, ...

I'll look into resurrecting another branch I made in the past which implements a generic FoldLeft function and reimplements all of the above on top of it, which would make it much easier to implement this atop.

[fingolfin]

Regarding documentation, also List for a collection is not correctly documented: it omits the possibility to specify a function which is applied to all elements of the collection. Because List has two manual entries, one for lists and one for collections. This is unlike Filtered, Sum, etc., which all merge this into a single reference manual entry.

[markuspf]

I'll just merge this, everything else can be done in later PRs anyway.