Find packages in active 'parent'/global projects too

[tfiers]

originally from

DepGraphs.is_in_project is not enough: it can also be importable if in a parent project
(hm, maybe depgraphs should look into parent/global projects too)

from

• time_imports: handle when pkg not found #101 (comment).

Has sth to do w/

julia> LOAD_PATH
3-element Vector{String}:
 "@"
 "@v#.#"
 "@stdlib"

[tfiers]

So maybe: is_in_project → is_loadable