Improve documentation of propertynames (#46621)

refer to `property names` not `fieldnames`

Author: bkamins

base/reflection.jl

@@ -1838,7 +1838,7 @@ as well to get the properties of an instance of the type.
 
 `propertynames(x)` may return only "public" property names that are part
 of the documented interface of `x`.   If you want it to also return "private"
-fieldnames intended for internal use, pass `true` for the optional second argument.
+property names intended for internal use, pass `true` for the optional second argument.
 REPL tab completion on `x.` shows only the `private=false` properties.
 
 See also: [`hasproperty`](@ref), [`hasfield`](@ref).

doc/src/manual/interfaces.md

@@ -739,7 +739,7 @@ in one or two dimensional outputs, but produce an `Array` for any other dimensio
 
 | Methods to implement              | Default definition           | Brief description                                                                     |
 |:--------------------------------- |:---------------------------- |:------------------------------------------------------------------------------------- |
-| `propertynames(x::ObjType, private::Bool=false)` | `fieldnames(typeof((x))`     | Return a tuple of the properties (`x.property`) of an object `x`. If `private=true`, also return fieldnames intended to be kept as private |
+| `propertynames(x::ObjType, private::Bool=false)` | `fieldnames(typeof(x))`     | Return a tuple of the properties (`x.property`) of an object `x`. If `private=true`, also return property names intended to be kept as private |
 | `getproperty(x::ObjType, s::Symbol)`       | `getfield(x, s)`     | Return property `s` of `x`. `x.s` calls `getproperty(x, :s)`.  |
 | `setproperty!(x::ObjType, s::Symbol, v)`   | `setfield!(x, s, v)` | Set property `s` of `x` to `v`. `x.s = v` calls `setproperty!(x, :s, v)`. Should return `v`.|