Enhance docs on type piracy

[lgoettgens]

I would really like to have some enhanced documentation on type piracy, with some examples, common pitfalls, and maybe even ways to reorganize code to circumvent it.
I am unsure if this fits into https://docs.julialang.org/en/v1/manual/style-guide/#Avoid-type-piracy or should be placed somewhere else.

@mateuszbaran and @LilithHafner already contributed some relevant cases to cover in a discussion on automated type piracy detection in Aqua.jl (JuliaTesting/Aqua.jl#173 (comment)), but I think it would be better to have it in the official julia docs.

In particular, some information about foo(Vector{<:SomeAbstractType}) adding a dispatch of the form foo(Vector{Union{}}) would be great. (x-ref Nemocas/AbstractAlgebra.jl#1466). See also #33780