feat(webpack): read nativescript.config.ts main if set before fallback to package.json (#9769)

implements #9658

BREAKING CHANGES:

Possibly breaking if a project has a main field set in the nativescript.config.ts - since after this lands, this value will be used instead of package.json main.

The impact is likely very small, the steps to migrate:

    (Option A) remove main from nativescript.config.ts if set
    (Option B) update main to the correct path in nativescript.config.ts if set incorrectly

packages/webpack5/__tests__/helpers/platform.spec.ts

@@ -0,0 +1,49 @@
+import { env } from '../../src/';
+import { addPlatform, getEntryPath } from '../../src/helpers/platform';
+
+import { getValue } from '../../src/helpers/config';
+
+describe('getEntryPath', () => {
+	it('uses platform getEntryPath if the platform specifies it', () => {
+		env.platform = 'testPlatform';
+		addPlatform('testPlatform', {
+			getEntryPath() {
+				return 'custom-entry-path';
+			},
+		});
+
+		const res = getEntryPath();
+		expect(res).toEqual('custom-entry-path');
+
+		// cleanup env
+		delete env.platform;
+	});
+
+	it('uses main from nativescript.config.ts if set', () => {
+		env.ios = true;
+
+		// mock getValue
+		const getValueMock = getValue as jest.Mock;
+		const getValueMockImpl = getValueMock.getMockImplementation();
+
+		getValueMock.mockImplementation((key) => {
+			if (key === 'main') {
+				return 'main-from-config';
+			}
+		});
+
+		const res = getEntryPath();
+		expect(res).toEqual('__jest__/main-from-config');
+
+		// reset mock implementation
+		getValueMock.mockImplementation(getValueMockImpl);
+	});
+
+	it('uses main from package.json', () => {
+		env.ios = true;
+
+		const res = getEntryPath();
+		// set in jest.setup.ts mock for package.json...
+		expect(res).toEqual('__jest__/src/app.js');
+	});
+});