fix(ivy): use a single constant pool per source file (#25392)

Previously, ngtsc used a new ConstantPool for each decorator
compilation. This could result in collisions between constants in the
top-level scope.

Now, ngtsc uses a single ConstantPool for each source file being
compiled, and merges the constant statements into the file after the
import section.

PR Close #25392

packages/compiler-cli/src/ngcc/test/rendering/esm2015_renderer_spec.ts

@@ -56,6 +56,36 @@ A.decorators = [
   });
 
 
+  describe('addConstants', () => {
+    it('should insert the given constants after imports in the source file', () => {
+      const PROGRAM = {
+        name: 'some/file.js',
+        contents: `
+/* A copyright notice */
+import {Directive} from '@angular/core';
+export class A {}
+A.decorators = [
+  { type: Directive, args: [{ selector: '[a]' }] },
+  { type: Other }
+];
+// Some other content`
+      };
+      const {renderer, program} = setup(PROGRAM);
+      const file = program.getSourceFile('some/file.js');
+      if (file === undefined) {
+        throw new Error(`Could not find source file`);
+      }
+      const output = new MagicString(PROGRAM.contents);
+      renderer.addConstants(output, 'const x = 3;', file);
+      expect(output.toString()).toContain(`
+import {Directive} from '@angular/core';
+const x = 3;
+
+export class A {}`);
+    });
+  });
+
+
   describe('addDefinitions', () => {
     it('should insert the definitions directly after the class declaration', () => {
       const PROGRAM = {

packages/compiler-cli/src/ngcc/test/rendering/renderer_spec.ts

@@ -20,6 +20,9 @@ class TestRenderer extends Renderer {
   addImports(output: MagicString, imports: {name: string, as: string}[]) {
     output.prepend('\n// ADD IMPORTS\n');
   }
+  addConstants(output: MagicString, constants: string, file: ts.SourceFile): void {
+    output.prepend('\n// ADD CONSTANTS\n');
+  }
   addDefinitions(output: MagicString, analyzedClass: AnalyzedClass, definitions: string) {
     output.prepend('\n// ADD DEFINITIONS\n');
   }
@@ -65,7 +68,8 @@ describe('Renderer', () => {
     ]
   });
   const RENDERED_CONTENTS =
-      `\n// REMOVE DECORATORS\n\n// ADD IMPORTS\n\n// ADD DEFINITIONS\n` + INPUT_PROGRAM.contents;
+      `\n// REMOVE DECORATORS\n\n// ADD IMPORTS\n\n// ADD CONSTANTS\n\n// ADD DEFINITIONS\n` +
+      INPUT_PROGRAM.contents;
   const OUTPUT_PROGRAM_MAP = fromObject({
     'version': 3,
     'file': '/output_file.js',
@@ -74,14 +78,14 @@ describe('Renderer', () => {
       'import { Directive } from \'@angular/core\';\nexport class A {\n    foo(x) {\n        return x;\n    }\n}\nA.decorators = [\n    { type: Directive, args: [{ selector: \'[a]\' }] }\n];\n'
     ],
     'names': [],
-    'mappings': ';;;;;;AAAA;;;;;;;;;'
+    'mappings': ';;;;;;;;AAAA;;;;;;;;;'
   });
 
   const MERGED_OUTPUT_PROGRAM_MAP = fromObject({
     'version': 3,
     'sources': ['/file.ts'],
     'names': [],
-    'mappings': ';;;;;;AAAA',
+    'mappings': ';;;;;;;;AAAA',
     'file': '/output_file.js',
     'sourcesContent': [
       'import { Directive } from \'@angular/core\';\nexport class A {\n    foo(x: string): string {\n        return x;\n    }\n    static decorators = [\n        { type: Directive, args: [{ selector: \'[a]\' }] }\n    ];\n}'