Bad docstring path/linenumber if in macro call

[mortenpi]

The filename and line numbers for a docstring are not properly stored if the definition is wrapped in a macro call, e.g. in the following case:

"""
    struct A
"""
Base.@kwdef struct A
  a::Int = 1
end

For an MWE, include-ing this:

"""
    struct A
"""
Base.@kwdef struct A
  a::Int = 1
end

"""
    struct B
"""
struct B
  a::Int
end

Base.@kwdef struct C
  a::Int = 1
end

@doc """
    struct C
""" C

will lead to this when fetching the docstring metadata (note the missing :path and :linenumber for A):

julia> @doc(A).meta[:results][1].data
Dict{Symbol,Any} with 6 entries:
  :typesig    => Union{}
  :module     => Main
  :linenumber => 0
  :binding    => A
  :path       => ""
  :fields     => Dict{Any,Any}()

julia> @doc(B).meta[:results][1].data
Dict{Symbol,Any} with 6 entries:
  :typesig    => Union{}
  :module     => Main
  :linenumber => 14
  :binding    => B
  :path       => "/home/mortenpi/Julia/test/test.jl"
  :fields     => Dict{Any,Any}()

julia> @doc(C).meta[:results][1].data
Dict{Symbol,Any} with 5 entries:
  :typesig    => Union{}
  :module     => Main
  :linenumber => 25
  :binding    => C
  :path       => "/home/mortenpi/Julia/test/test.jl"

X-ref: JuliaDocs/Documenter.jl#1374

[bzinberg]

The C solution loses field docstrings: after changing the included code to

"""
    struct A
"""
Base.@kwdef struct A
  """A well-documented integer."""
  a::Int = 1
end

"""
    struct B
"""
struct B
  """A well-documented integer."""
  a::Int
end

Base.@kwdef struct C
  """A well-documented integer."""
  a::Int = 1
end

@doc """
    struct C
""" C

we have

julia> @doc(A).meta[:results][1].data[:fields]
Dict{Symbol,String} with 1 entry:
  :a => "A well-documented integer."

julia> @doc(C).meta[:results][1].data[:fields]
ERROR: KeyError: key :fields not found
Stacktrace:
 [1] getindex(::Dict{Symbol,Any}, ::Symbol) at ./dict.jl:477
 [2] top-level scope at REPL[3]:1