Add lexical scope and redefining variables in functions (#3015)

* Fix to allow variable shadowing inside functions

* Implement closures

* Fix KCL test code to not reference future tag definition

* Remove tag declarator from function parameters

This is an example where the scoping change revealed a subtle issue
with TagDeclarators.  You cannot bind a new tag using a function
parameter.

The issue is that evaluating a TagDeclarator like $foo binds an
identifier to its corresponding TagIdentifier, but returns the
TagDeclarator.  If you have a TagDeclarator passed in as a parameter
to a function, you can never get its corresponding TagIdentifier.

This seems like a case where TagDeclarator evaluation needs to be
revisited, especially now that we have scoped tags.

* Fix to query return, functions, and tag declarator AST nodes correctly

src/lib/testHelpers.ts

@@ -75,7 +75,7 @@ class MockEngineCommandManager {
 
 export async function enginelessExecutor(
   ast: Program | Error,
-  pm: ProgramMemory | Error = { root: {}, return: null }
+  pm: ProgramMemory | Error = ProgramMemory.empty()
 ): Promise<ProgramMemory> {
   if (err(ast)) return Promise.reject(ast)
   if (err(pm)) return Promise.reject(pm)
@@ -93,7 +93,7 @@ export async function enginelessExecutor(
 
 export async function executor(
   ast: Program,
-  pm: ProgramMemory = { root: {}, return: null }
+  pm: ProgramMemory = ProgramMemory.empty()
 ): Promise<ProgramMemory> {
   const engineCommandManager = new EngineCommandManager()
   engineCommandManager.start({