Revert "Make algebraic sets and varieties internal (#2424)"

[thofma]

This reverts commit e2e2c31.

[thofma]

Should be merged right after #2429.

CC: @simonbrandhorst

[codecov]

Codecov Report

Merging #2430 (46f0bf9) into master (e2e2c31) will increase coverage by 0.17%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2430      +/-   ##
==========================================
+ Coverage   71.48%   71.65%   +0.17%     
==========================================
  Files         392      392              
  Lines       52831    52831              
==========================================
+ Hits        37765    37855      +90     
+ Misses      15066    14976      -90     

Impacted Files	Coverage Δ
...Schemes/AffineAlgebraicSet/Objects/Constructors.jl	35.89% <ø> (+35.89%)	⬆️
...etry/Schemes/AffineVariety/Objects/Constructors.jl	94.11% <ø> (+70.58%)	⬆️
...mes/ProjectiveAlgebraicSet/Objects/Constructors.jl	44.44% <ø> (+44.44%)	⬆️
.../Schemes/ProjectiveVariety/Objects/Constructors.jl	64.51% <ø> (+45.16%)	⬆️

... and 11 files with indirect coverage changes