Fix compiler bug with nested optional arguments

This commit fixes compiler bug where it fails when optional values are
compiled into absent values in nested calls.

- Throw exception with more context for easier future debugging.
- Add better validation of argument values for nested calls.
- Refactor `FunctionCallCompiler` for better clarity and modularize it
  to make it more maintainable and testable.
- Refactor related interface to not have `I` prefix, and
  function/variable names for better clarity.

Context:

Discovered this issue while attempting to call
`RunInlineCodeAsTrustedInstaller` which in turn invokes `RunPowerShell`
for issue #246. This led to the realization that despite parameters
flagged as optional, the nested argument compilation didn't support
them.

src/application/Parser/Script/Compiler/Function/ISharedFunction.ts

@@ -1,5 +1,5 @@
 import { IReadOnlyFunctionParameterCollection } from './Parameter/IFunctionParameterCollection';
-import { IFunctionCall } from './Call/IFunctionCall';
+import { FunctionCall } from './Call/FunctionCall';
 
 export interface ISharedFunction {
   readonly name: string;
@@ -9,8 +9,8 @@ export interface ISharedFunction {
 
 export interface ISharedFunctionBody {
   readonly type: FunctionBodyType;
-  readonly code: IFunctionCode;
-  readonly calls: readonly IFunctionCall[];
+  readonly code: IFunctionCode | undefined;
+  readonly calls: readonly FunctionCall[] | undefined;
 }
 
 export enum FunctionBodyType {