Add uplo check to Bidiagonal, Symmetric, and Hermitian base constructors

[mcognetta]

Currently, most, but not all, constructors for Bidiagonal, Symmetric, and Hermitian matrices perform an uplo check to see if it is valid (U/:U or L/:L). However, the base constructors do not.

This PR adds an uplo check to the base constructors and slightly expands the throw_uplo error message.

---

For example,

At HEAD:

julia> Bidiagonal(rand(2), rand(1), 'U')
2×2 Bidiagonal{Float64,Array{Float64,1}}:
 0.792414  0.848267
  ⋅        0.0463521

julia> Bidiagonal(rand(2), rand(1), 'X')
2×2 Bidiagonal{Float64,Array{Float64,1}}:
 0.916971   ⋅ 
 0.0       0.27176

julia> Bidiagonal(rand(2), rand(1), :U)
2×2 Bidiagonal{Float64,Array{Float64,1}}:
 0.810733  0.828368
  ⋅        0.628955

julia> Bidiagonal(rand(2), rand(1), :X)
ERROR: ArgumentError: uplo argument must be either :U (upper) or :L (lower)
Stacktrace:
 [1] throw_uplo() at /home/mc/github/julia/usr/share/julia/stdlib/v1.5/LinearAlgebra/src/LinearAlgebra.jl:257
 [2] char_uplo at /home/mc/github/julia/usr/share/julia/stdlib/v1.5/LinearAlgebra/src/LinearAlgebra.jl:242 [inlined]
 [3] Bidiagonal(::Array{Float64,1}, ::Array{Float64,1}, ::Symbol) at /home/mc/github/julia/usr/share/julia/stdlib/v1.5/LinearAlgebra/src/bidiag.jl:65
 [4] top-level scope at REPL[6]:1

This PR:

julia> Bidiagonal(rand(2), rand(1), 'U')
2×2 Bidiagonal{Float64, Vector{Float64}}:
 0.970627  0.828208
  ⋅        0.265786

julia> Bidiagonal(rand(2), rand(1), 'X')
ERROR: ArgumentError: uplo argument must be either :U/'U' (upper) or :L/'L' (lower)
Stacktrace:
 [1] throw_uplo()
   @ LinearAlgebra ~/github/julia-dev/usr/share/julia/stdlib/v1.8/LinearAlgebra/src/LinearAlgebra.jl:265
 [2] Bidiagonal{Float64, Vector{Float64}}(dv::Vector{Float64}, ev::Vector{Float64}, uplo::Char)
   @ LinearAlgebra ~/github/julia-dev/usr/share/julia/stdlib/v1.8/LinearAlgebra/src/bidiag.jl:13
 [3] Bidiagonal(dv::Vector{Float64}, ev::Vector{Float64}, uplo::Char)
   @ LinearAlgebra ~/github/julia-dev/usr/share/julia/stdlib/v1.8/LinearAlgebra/src/bidiag.jl:69
 [4] top-level scope
   @ REPL[3]:1

julia> Bidiagonal(rand(2), rand(1), :U)
2×2 Bidiagonal{Float64, Vector{Float64}}:
 0.768898  0.461265
  ⋅        0.409974

julia> Bidiagonal(rand(2), rand(1), :X)
ERROR: ArgumentError: uplo argument must be either :U/'U' (upper) or :L/'L' (lower)
Stacktrace:
 [1] throw_uplo()
   @ LinearAlgebra ~/github/julia-dev/usr/share/julia/stdlib/v1.8/LinearAlgebra/src/LinearAlgebra.jl:265
 [2] char_uplo
   @ ~/github/julia-dev/usr/share/julia/stdlib/v1.8/LinearAlgebra/src/LinearAlgebra.jl:251 [inlined]
 [3] Bidiagonal
   @ ~/github/julia-dev/usr/share/julia/stdlib/v1.8/LinearAlgebra/src/bidiag.jl:18 [inlined]
 [4] Bidiagonal(dv::Vector{Float64}, ev::Vector{Float64}, uplo::Symbol)
   @ LinearAlgebra ~/github/julia-dev/usr/share/julia/stdlib/v1.8/LinearAlgebra/src/bidiag.jl:76
 [5] top-level scope
   @ REPL[5]:1

And likewise for Symmetric and Hermitian.

[mcognetta]

Buildbot errors seem unrelated.

[dkarrasch]

@andreasnoack I guess this change here should be reverted according to your comment that the Char representation is internal? The additional checks in this PR should be fine, though.

[andreasnoack]

Yeah. I'd think so. At least temporarily until a decision has been made.