Backports to v1.12

[dkarrasch]

• Revert "Use BLAS.trsm! instead of LAPACK.trtrs! in left-triangular solves" #1239
• Fix 3-arg dot for empty arrays #1485
• Fix forgotten conj(alpha) in her2k documentation #1480
• Fixed typo in matmul.jl #1492
• Make dot consistently return zero on empty arrays #1494

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.63%. Comparing base (5567504) to head (b17cd17).

Files with missing lines	Patch %	Lines
src/triangular.jl	42.85%	4 Missing ⚠️
src/hessenberg.jl	0.00%	1 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff                @@
##           release-1.12    #1490      +/-   ##
================================================
+ Coverage         93.56%   93.63%   +0.06%     
================================================
  Files                34       34              
  Lines             15487    15481       -6     
================================================
+ Hits              14490    14495       +5     
+ Misses              997      986      -11     

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[dkarrasch]

Why can't I make a merge commit? It only offers "Squash and merge", but we don't squash backports commits, do we?

@KristofferC @ViralBShah