Code clean and reuse for constructor.

[N5N3]

Seperated from #1009.

This PR aims to unify the implement of StaticArray's constructor with a new method construct_type.
It returns a concrete constructor based on src <: Union{Tupe, StaticArray, AbstractArray} and the target type SA (if possible).
e.g.

julia> StaticArrays.construct_type(SMatrix{2},(1,2,3,4))
SMatrix{2, 2, Int64} (alias for SArray{Tuple{2, 2}, Int64, 2})

julia> StaticArrays.construct_type(SMatrix{2},(1.,2,3,4))
SMatrix{2, 2, Float64} (alias for SArray{Tuple{2, 2}, Float64, 2})

julia> StaticArrays.construct_type(SMatrix,(1.,2,3,4)) # the output's size is not static.
ERROR: DimensionMismatch: No precise constructor for SMatrix found. Length of input was 4.

Thus, we only need to mannually define the constructor with precise size, eltype and ndims.
Unneeded dispatch has been removed.
Edit1: Since 3rd party StaticArray might prefer previous design, the default construct_type returns the input SA directly to keep compatibility.
Edit2: construct_type for FieldArray has been implemented. Now FieldArray's default constructor support eltype promotion.

julia> struct Point2D{T} <: FieldVector{2,T}
           x::T
           y::T
       end

julia> Point2D(1,1.0)
2-element Point2D{Float64} with indices SOneTo(2):
 1.0
 1.0

This PR also restrict the input wrapping within constructor.
If multiple arguments are provided, all of them should be treated as the result's elements, and re-wrapping is not allowed anymore.
For example

julia> Scalar(1, 2)
ERROR: DimensionMismatch: No precise constructor for Scalar found. Length of input was 2.
julia> Scalar((1, 2))
Scalar{Tuple{Int64, Int64}}(((1, 2),))
julia> SVector{1}(1, 2)
ERROR: DimensionMismatch: No precise constructor for SVector{1} found. Length of input was 2.
julia> SVector{1}((1, 2))
1-element SVector{1, Tuple{Int64, Int64}} with indices SOneTo(1):
 (1, 2)

Close #809.
Close #911. (fix constructor missing)

[sjkelly]

🎆

[hyrodium]

Most of the changes seem great! I have added some comments.

[oscardssmith]

Is this ready to merge?

[N5N3]

I've added a warning to construct_type's docstring that invalid overload of this function might cause infinite recursion.
The main concern might be the influence on downside packages.
The default behavior should be exactly the same, but I only test this PR with Rotations.jl, Geodesy.jl.

[hyrodium]

Sorry for the late review. The rest of the code looks great to me.