verilog: Support module-scoped task/function calls

This is primarily intended to enable the standard-permitted use of
module-scoped identifiers to refer to tasks and non-constant functions.
As a side-effect, this also adds support for the non-standard use of
module-scoped identifiers referring to constant functions, a feature
that is supported in some other tools, including Iverilog.

CHANGELOG

@@ -9,6 +9,9 @@ Yosys 0.22 .. Yosys 0.22-dev
       Setting it to 1 causes abort() to be called when Yosys terminates with an
       error message.
 
+ * Verilog
+    - Support for module-scoped identifiers referring to tasks and functions.
+
 Yosys 0.21 .. Yosys 0.22
 --------------------------
  * Verific support