Out-of-place copytri in dense trig functions

[jishnub]

With this, the trig functions work for SMatrixes that don't support setindex!.

julia> S = SMatrix{4,4}(Symmetric(rand(4,4)))
4×4 SMatrix{4, 4, Float64, 16} with indices SOneTo(4)×SOneTo(4):
 0.470973   0.212605   0.0227701  0.744485
 0.212605   0.9227     0.022621   0.0139553
 0.0227701  0.022621   0.0568546  0.767089
 0.744485   0.0139553  0.767089   0.186663

julia> sin(S)
4×4 SMatrix{4, 4, Float64, 16} with indices SOneTo(4)×SOneTo(4):
  0.343589   0.140232    -0.044186     0.566605
  0.140232   0.781448    -0.00290253  -0.0305854
 -0.044186  -0.00290253   0.027389     0.623148
  0.566605  -0.0305854    0.623148     0.0739855

There are some type-inference issues at present, as applydiagonal returns a mutable array, but these may be addressed separately.

[codecov]

Codecov Report

Attention: Patch coverage is 98.03922% with 1 line in your changes missing coverage. Please review.

Project coverage is 91.97%. Comparing base (579b5f7) to head (e63635c).
Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
src/dense.jl	98.03%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1224      +/-   ##
==========================================
+ Coverage   91.93%   91.97%   +0.04%     
==========================================
  Files          34       34              
  Lines       15384    15415      +31     
==========================================
+ Hits        14143    14178      +35     
+ Misses       1241     1237       -4     

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