Docs expand using parameters (#21076)

* Trying to fix by changing renderer

* add renderExpandUsing flag

This flag makes the renderer expand parameters that use using statement to have their full type

* Update docs

* Make comment better explain why checking for nkSym

* Fix nil access when macro/template has parameter with no type

* Fix nil access when node is not semmed yet

nimdoc/testproject/testproject.nim

@@ -42,6 +42,11 @@ proc buzz*[T](a, b: T): T {.deprecated: "since v0.20".} =
 type
   FooBuzz* {.deprecated: "FooBuzz msg".} = int
 
+using f: FooBuzz
+
+proc bar*(f) = # `f` should be expanded to `f: FooBuzz`
+  discard
+
 import std/macros
 
 var aVariable*: array[1, int]