build: fix paths to typings files so tsickle resolves imports correctly

Fixes #15080

tools/public_api_guard/compiler/testing.d.ts

@@ -0,0 +1,44 @@
+export declare class MockDirectiveResolver extends DirectiveResolver {
+    constructor(_injector: Injector);
+    resolve(type: Type): DirectiveMetadata;
+    setProvidersOverride(type: Type, providers: any[]): void;
+    setViewProvidersOverride(type: Type, viewProviders: any[]): void;
+}
+
+export declare class MockSchemaRegistry implements ElementSchemaRegistry {
+    attrPropMapping: {
+        [key: string]: string;
+    };
+    existingProperties: {
+        [key: string]: boolean;
+    };
+    constructor(existingProperties: {
+        [key: string]: boolean;
+    }, attrPropMapping: {
+        [key: string]: string;
+    });
+    getMappedPropName(attrName: string): string;
+    hasProperty(tagName: string, property: string): boolean;
+    securityContext(tagName: string, property: string): SecurityContext;
+}
+
+export declare class MockViewResolver extends ViewResolver {
+    constructor(_injector: Injector);
+    overrideViewDirective(component: Type, from: Type, to: Type): void;
+    resolve(component: Type): ViewMetadata;
+    setAnimations(component: Type, animations: AnimationEntryMetadata[]): void;
+    setInlineTemplate(component: Type, template: string): void;
+    setView(component: Type, view: ViewMetadata): void;
+}
+
+export declare class OverridingTestComponentBuilder extends TestComponentBuilder {
+    constructor(injector: Injector);
+    createAsync<T>(rootComponentType: ConcreteType<T>): Promise<ComponentFixture<T>>;
+    createSync<T>(rootComponentType: ConcreteType<T>): ComponentFixture<T>;
+    overrideAnimations(componentType: Type, animations: AnimationEntryMetadata[]): TestComponentBuilder;
+    overrideDirective(componentType: Type, from: Type, to: Type): OverridingTestComponentBuilder;
+    overrideProviders(type: Type, providers: any[]): OverridingTestComponentBuilder;
+    overrideTemplate(componentType: Type, template: string): OverridingTestComponentBuilder;
+    overrideView(componentType: Type, view: ViewMetadata): OverridingTestComponentBuilder;
+    overrideViewProviders(type: Type, providers: any[]): OverridingTestComponentBuilder;
+}