Add/unify broadcast in mul! with Diagonal #761

Job	Run time
Documentation	1m 16s
OpenCL.jl	17m 12s
Julia 1.10 - ubuntu-latest - x64	9m 18s
Julia 1.10 - macOS-latest - x64	11m 40s
Julia 1.10 - windows-latest - x64	10m 8s
Julia pre - ubuntu-latest - x64	12m 12s
Julia pre - macOS-latest - x64	17m 3s
Julia pre - windows-latest - x64	13m 16s
Julia nightly - ubuntu-latest - x64	10m 31s
Julia nightly - macOS-latest - x64	17m 16s
Julia nightly - windows-latest - x64	11m 34s
	2h 11m 26s

Provide feedback