Add MakeImm and Imm

[ChrisJefferson]

This adds two shorthands, MakeImm for MakeImmutable, and Imm for Immutable. These are because we want to call these functions a lot in HPC-GAP, and so having shorter names is useful.

[codecov]

Codecov Report

Merging #1333 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1333      +/-   ##
==========================================
- Coverage   61.48%   61.47%   -0.01%     
==========================================
  Files        1049     1049              
  Lines      365572   365471     -101     
  Branches    15163    15129      -34     
==========================================
- Hits       224755   224661      -94     
- Misses     136797   136802       +5     
+ Partials     4020     4008      -12

Impacted Files	Coverage Δ
lib/object.gd	50% <ø> (ø)	⬆️
hpcgap/lib/object.gd	50% <ø> (ø)	⬆️
lib/files.gi	36.47% <0%> (-17.63%)	⬇️
lib/files.gd	56.98% <0%> (-5.38%)	⬇️
src/system.c	51.03% <0%> (-3.06%)	⬇️
src/objects.h	68.42% <0%> (-2.42%)	⬇️
hpcgap/pkg/gapdoc/PackageInfo.g	33.33% <0%> (-1.29%)	⬇️
lib/pager.gi	7.27% <0%> (-0.61%)	⬇️
lib/init.g	45.38% <0%> (-0.28%)	⬇️
src/funcs.c	63.92% <0%> (-0.14%)	⬇️
... and 6 more

[olexandr-konovalov]

This is reverted in master in #2122 and cherry-picked onto stable-4.9. Removed mentioning this from the release notes for GAP 4.9.