Make ScopedValues.get a method of Base.get

[LilithHafner]

Implements #54553

[KristofferC]

There is no docs for what the generic concept for a two arg get is so that needs to be established first? The docs for get only list the three arg version for example.

[LilithHafner]

Why is 2-arg get relevant to this PR?

julia> methods(Base.ScopedValues.get)
# 1 method for generic function "get" from Base.ScopedValues:
 [1] get(val::Base.ScopedValues.ScopedValue{T}) where T
     @ scopedvalues.jl:151

[KristofferC]

2->1 then :P

[LilithHafner]

The only 1-arg method is documented as

    get(val::ScopedValue{T})::Union{Nothing, Some{T}}

If the scoped value isn't set and doesn't have a default value,
return `nothing`. Otherwise returns `Some{T}` with the current
value.

The generic concept of a 1-arg get is

    get(x) -> Union{Some, Nothing}

If `x` has a value, return `Some` with that value, otherwise return `nothing`.

How/where would you like that documented?

[KristofferC]

Just so the generic meaning shows up when one checks the help for it, just like any other method. Otherwise, you cannot extend this arity of the function since you don't know what it means.

In fact, it is preferable to just have the generic method documented, then there is no need to write an implementation specific docstring for the ScopedValue version. Could it be documented as:

"""
    get(x) -> Union{Some, Nothing}

If `x` has a value, return `Some` with that value, otherwise return `nothing`.
"""
function get(x) end

?

[KristofferC]

Otherwise returns Some{T} with the current value.

Nit, should be "return"