refactor(compiler-cli): implement BabelAstFactory and AstHosts (#38866)

This commit adds the `AstHost` interface, along with implementations for
both Babel and TS.

It also implements the Babel vesion of the `AstFactory` interface, along
with a linker specific implementation of the `ImportGenerator` interface.

These classes will be used by the new "ng-linker" to transform prelinked
library code using a Babel plugin.

PR Close #38866

packages/compiler-cli/src/ngtsc/translator/index.ts

@@ -6,7 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-export {AstFactory, BinaryOperator, LeadingComment, ObjectLiteralProperty, SourceMapLocation, SourceMapRange, TemplateElement, TemplateLiteral, UnaryOperator} from './src/api/ast_factory';
+export {AstFactory, BinaryOperator, LeadingComment, ObjectLiteralProperty, SourceMapLocation, SourceMapRange, TemplateElement, TemplateLiteral, UnaryOperator, VariableDeclarationType} from './src/api/ast_factory';
 export {Import, ImportGenerator, NamedImport} from './src/api/import_generator';
 export {ImportManager} from './src/import_manager';
 export {RecordWrappedNodeExprFn} from './src/translator';

packages/compiler-cli/src/ngtsc/translator/src/api/ast_factory.ts

@@ -21,7 +21,7 @@ export interface AstFactory<TStatement, TExpression> {
    * @param leadingComments the comments to attach.
    * @returns the node passed in as `statement` with the comments attached.
    */
-  attachComments(statement: TStatement, leadingComments?: LeadingComment[]): TStatement;
+  attachComments(statement: TStatement, leadingComments: LeadingComment[]|undefined): TStatement;
 
   /**
    * Create a literal array expresion (e.g. `[expr1, expr2]`).

packages/compiler-cli/src/ngtsc/translator/src/typescript_ast_factory.ts

@@ -235,7 +235,7 @@ export function createTemplateTail(cooked: string, raw: string): ts.TemplateTail
  * @param leadingComments The comments to attach to the statement.
  */
 export function attachComments<T extends ts.Statement>(
-    statement: T, leadingComments?: LeadingComment[]): T {
+    statement: T, leadingComments: LeadingComment[]|undefined): T {
   if (leadingComments === undefined) {
     return statement;
   }