reflection: allow `names` to return `using`-ed names (#54609)
This commit makes it possible for `names` to return `using`-ed names as
well:
```julia
julia> using Base: @assume_effects
julia> Symbol("@assume_effects") in names(@__MODULE__; usings=true)
true
```
Currently, to find all names available in a module `A`, the following
steps are needed:
1. Use `names(A; all=true, imported=true)` to get the names defined by
`A` and the names explicitly `import`ed by `A`.
2. Use `jl_module_usings(A)` to get the list of modules `A` has
`using`-ed and then use `names()` to get the names `export`ed by those
modules.
This method is implemented in e.g. REPL completions, but it has a
problem: it could not get the names explicitly `using`-ed by `using B:
...` (#36529, #40356, JuliaDebug/Infiltrator.jl#106, etc.).
This commit adds a new keyword argument `usings::Bool=false` to
`names(A; ...)`, which, when `usings=true` is specified, returns all
names introduced by `using` in `A`.
In other words, `usings=true` not only returns explicitly `using`-ed
names but also incorporates step 2 above into the implementation of
`names`.
By using this new option, we can now use
`names(A; all=true, imported=true, usings=true)` to know all names
available in `A`, without implementing the two-fold steps on application
side.
As example application, this new feature will be used to simplify and
enhance the implementation of REPL completions.
- fixes #36529
Co-authored-by: Nathan Daly <NHDaly@gmail.com>
Co-authored-by: Sebastian Pfitzner <pfitzseb@gmail.com>
