Matrix groups: cleanup some use of frobenius

[fingolfin]

Also added a comment on how conjugate_transpose could be
made more efficient if needed

[mjrodgers]

I think this looks good, I can talk to @fieker about updating to precompute the Frobenius map if this is an improvement we should make but in the meantime I think this should be merged (modulo the tests passing, looking at those now).

[mjrodgers]

Have another error I'm trying to straighten out still, getting a BoundsError from conjugate_transpose with this one:

F,a = finite_field(3,2,"a")
x = diagonal_matrix(F.([1,2,1,1,1]))
y = diagonal_matrix(F.([2,1,0,0,2]))
y[3,4]=a; y[4,3]=a^3; y[4,5]=1+a; y[5,4]=(1+a)^3;
f = hermitian_form(x); g = hermitian_form(y)
is_true,z = is_congruent(f,g)

[mjrodgers]

Have another error I'm trying to straighten out

OK I think this is resolved too, if the rest of the tests pass I think this can be merged now.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.65%. Comparing base (224cb53) to head (790e02c).
Report is 6 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4079   +/-   ##
=======================================
  Coverage   84.64%   84.65%           
=======================================
  Files         612      614    +2     
  Lines       83240    83332   +92     
=======================================
+ Hits        70460    70543   +83     
- Misses      12780    12789    +9     

Files with missing lines	Coverage Δ
src/Groups/matrices/matrix_manipulation.jl	97.40% <100.00%> (+0.10%)	⬆️
src/Groups/matrices/transform_form.jl	98.51% <100.00%> (+0.02%)	⬆️

... and 14 files with indirect coverage changes

[fingolfin]

Thank you all for brining my shoddy PR over the finishing line :-)