[ToricVarieties] Overhaul equality of normal toric varieties

[HereAround]

This PR aims to close #3934 as follows:

• Overwrite the == method: Return true if === is true and otherwise raise an error.
• Add documentation which explains why this computation is very demanding.
• Add a (stupid) (as in not very performant) equality method slow_equal. I have not exported this method (exports are hard to revert, we do not want anybody to use this method unless they really, really want to etc.). Still, the method is documented.
• Throughout OSCAR, == of two toric varieties was used in a number of places. It seemed reasonable to change some of them to ===.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.01%. Comparing base (efd6412) to head (2f52348).
Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3946      +/-   ##
==========================================
+ Coverage   83.98%   84.01%   +0.02%     
==========================================
  Files         592      592              
  Lines       81635    81679      +44     
==========================================
+ Hits        68562    68620      +58     
+ Misses      13073    13059      -14     

Files	Coverage Δ
experimental/Schemes/src/IdealSheaves.jl	78.71% <100.00%> (+0.03%)	⬆️
...oricVarieties/NormalToricVarieties/constructors.jl	100.00% <100.00%> (ø)
...ebraicGeometry/ToricVarieties/Proj/constructors.jl	92.72% <100.00%> (ø)
...etry/ToricVarieties/ToricMorphisms/constructors.jl	67.85% <100.00%> (ø)

... and 8 files with indirect coverage changes