Avoid concatenating LazyString in setindex! for triangular matrices

[jishnub]

This PR changes operations like a::String * b::LazyString to LazyString(a, b), which avoids some runtime dispatches and plays better with JET. The changes are in the error paths of setindex! for AbstractTriangular matrices. This also reduces code duplication.

Specifically, this fixes the warnings in the following:
On v1.11:

julia> using LinearAlgebra

julia> using JET

julia> @report_opt eigen(Hermitian(rand(2,2)))
[ Info: tracking Base
┌ Warning: skipping var"#_#113"(kw::Base.Pairs{Symbol, V, NTuple{N, Symbol}, NamedTuple{names, T}} where {V, N, names, T<:NTuple{N, Any}}, c::ComposedFunction, x...) @ Base operators.jl:1050 to avoid parsing too much code
└ @ Revise ~/.julia/packages/Revise/bAgL0/src/packagedef.jl:1092
┌ Warning: skipping var"#sprint#594"(context, sizehint::Integer, ::typeof(sprint), f::Function, args...) @ Base strings/io.jl:107 to avoid parsing too much code
└ @ Revise ~/.julia/packages/Revise/bAgL0/src/packagedef.jl:1092
┌ Warning: skipping (::Base.var"#120#121")(io) @ Base strings/lazy.jl:84 to avoid parsing too much code
└ @ Revise ~/.julia/packages/Revise/bAgL0/src/packagedef.jl:1092
═════ 1 possible error found ═════
┌ eigen(A::Hermitian{Float64, Matrix{Float64}}) @ LinearAlgebra /cache/build/builder-amdci4-5/julialang/julia-release-1-dot-11/usr/share/julia/stdlib/v1.11/LinearAlgebra/src/symmetriceigen.jl:11
│┌ eigen(A::Hermitian{Float64, Matrix{Float64}}; sortby::Nothing) @ LinearAlgebra /cache/build/builder-amdci4-5/julialang/julia-release-1-dot-11/usr/share/julia/stdlib/v1.11/LinearAlgebra/src/symmetriceigen.jl:13
││┌ eigencopy_oftype(A::Hermitian{Float64, Matrix{Float64}}, S::Type{Float64}) @ LinearAlgebra /cache/build/builder-amdci4-5/julialang/julia-release-1-dot-11/usr/share/julia/stdlib/v1.11/LinearAlgebra/src/symmetriceigen.jl:4
│││┌ copy_similar(A::Hermitian{Float64, Matrix{Float64}}, ::Type{Float64}) @ LinearAlgebra /cache/build/builder-amdci4-5/julialang/julia-release-1-dot-11/usr/share/julia/stdlib/v1.11/LinearAlgebra/src/LinearAlgebra.jl:475
││││┌ copyto!(dest::Matrix{Float64}, src::Hermitian{Float64, Matrix{Float64}}) @ Base ./abstractarray.jl:1060
│││││┌ unalias(dest::Matrix{Float64}, A::Hermitian{Float64, Matrix{Float64}}) @ Base ./abstractarray.jl:1503
││││││┌ unaliascopy(A::Hermitian{Float64, Matrix{Float64}}) @ Base ./abstractarray.jl:1520
│││││││┌ copy(A::Hermitian{Float64, Matrix{Float64}}) @ LinearAlgebra /cache/build/builder-amdci4-5/julialang/julia-release-1-dot-11/usr/share/julia/stdlib/v1.11/LinearAlgebra/src/symmetric.jl:342
││││││││┌ parentof_applytri(f::typeof(copy), args::Hermitian{Float64, Matrix{Float64}}) @ LinearAlgebra /cache/build/builder-amdci4-5/julialang/julia-release-1-dot-11/usr/share/julia/stdlib/v1.11/LinearAlgebra/src/symmetric.jl:297
│││││││││┌ applytri(f::ComposedFunction{typeof(parent), typeof(copy)}, A::Hermitian{Float64, Matrix{Float64}}) @ LinearAlgebra /cache/build/builder-amdci4-5/julialang/julia-release-1-dot-11/usr/share/julia/stdlib/v1.11/LinearAlgebra/src/symmetric.jl:280
││││││││││┌ (::ComposedFunction{typeof(parent), typeof(copy)})(x::UpperTriangular{Float64, Matrix{Float64}}) @ Base ./operators.jl:1050
│││││││││││┌ (::ComposedFunction{typeof(parent), typeof(copy)})(x::UpperTriangular{Float64, Matrix{Float64}}; kw::@Kwargs{}) @ Base ./operators.jl:1050
││││││││││││┌ call_composed(fs::Tuple{typeof(parent), typeof(copy)}, x::Tuple{UpperTriangular{Float64, Matrix{…}}}, kw::@Kwargs{}) @ Base ./operators.jl:1053
│││││││││││││┌ call_composed(fs::Tuple{typeof(copy)}, x::Tuple{UpperTriangular{Float64, Matrix{Float64}}}, kw::@Kwargs{}) @ Base ./operators.jl:1054
││││││││││││││┌ copy(A::UpperTriangular{Float64, Matrix{Float64}}) @ LinearAlgebra /cache/build/builder-amdci4-5/julialang/julia-release-1-dot-11/usr/share/julia/stdlib/v1.11/LinearAlgebra/src/triangular.jl:183
│││││││││││││││┌ copyto!(A::UpperTriangular{Float64, Matrix{Float64}}, B::UpperTriangular{Float64, Matrix{Float64}}) @ LinearAlgebra /cache/build/builder-amdci4-5/julialang/julia-release-1-dot-11/usr/share/julia/stdlib/v1.11/LinearAlgebra/src/triangular.jl:520
││││││││││││││││┌ setindex!(A::UpperTriangular{Float64, Matrix{Float64}}, x::Float64, i::Int64, j::Int64) @ LinearAlgebra /cache/build/builder-amdci4-5/julialang/julia-release-1-dot-11/usr/share/julia/stdlib/v1.11/LinearAlgebra/src/triangular.jl:274
│││││││││││││││││┌ *(s1::String, ss::LazyString) @ Base ./strings/basic.jl:265
││││││││││││││││││┌ string(::String, ::LazyString) @ Base ./strings/io.jl:189
│││││││││││││││││││┌ print_to_string(::String, ::LazyString) @ Base ./strings/io.jl:148
││││││││││││││││││││┌ print(io::IOBuffer, s::LazyString) @ Base ./strings/io.jl:195
│││││││││││││││││││││┌ iterate(s::LazyString) @ Base ./strings/lazy.jl:94
││││││││││││││││││││││┌ String(l::LazyString) @ Base ./strings/lazy.jl:83
│││││││││││││││││││││││┌ sprint(::Base.var"#120#121"{LazyString}) @ Base ./strings/io.jl:107
││││││││││││││││││││││││┌ sprint(::Base.var"#120#121"{LazyString}; context::Nothing, sizehint::Int64) @ Base ./strings/io.jl:114
│││││││││││││││││││││││││┌ (::Base.var"#120#121"{LazyString})(io::IOBuffer) @ Base ./strings/lazy.jl:85
││││││││││││││││││││││││││ runtime dispatch detected: print(io::IOBuffer, %16::Any)::Any

With the changes from this PR

julia> @report_opt eigen(Hermitian(rand(2,2)))
No errors detected