PYTHONSTARTUP should be injected regardless of terminalEnv experiment (#25037)

Resolve: #25013 

Python shell integration env var injection via env var collection was
getting cleared undesirable, when user had opted out of terminal env var
experiment.

We want to inject PYTHONSTARTUP regardless of the experiment, depending
on user setting.

Author: anthonykim1

src/client/terminals/envCollectionActivation/service.ts

@@ -44,6 +44,7 @@ import {
 } from '../types';
 import { ProgressService } from '../../common/application/progressService';
 import { useEnvExtension } from '../../envExt/api.internal';
+import { registerPythonStartup } from '../pythonStartup';
 
 @injectable()
 export class TerminalEnvVarCollectionService implements IExtensionActivationService, ITerminalEnvVarCollectionService {
@@ -109,6 +110,7 @@ export class TerminalEnvVarCollectionService implements IExtensionActivationServ
                     );
                     this.registeredOnce = true;
                 }
+                await registerPythonStartup(this.context);
                 return;
             }
             if (!this.registeredOnce) {

src/test/interpreters/activation/terminalEnvVarCollectionService.unit.test.ts

@@ -6,12 +6,14 @@
 import * as sinon from 'sinon';
 import { assert, expect } from 'chai';
 import { mock, instance, when, anything, verify, reset } from 'ts-mockito';
+import * as TypeMoq from 'typemoq';
 import {
     EnvironmentVariableCollection,
     EnvironmentVariableMutatorOptions,
     GlobalEnvironmentVariableCollection,
     ProgressLocation,
     Uri,
+    WorkspaceConfiguration,
     WorkspaceFolder,
 } from 'vscode';
 import {
@@ -55,6 +57,7 @@ suite('Terminal Environment Variable Collection Service', () => {
     let terminalEnvVarCollectionService: TerminalEnvVarCollectionService;
     let terminalDeactivateService: ITerminalDeactivateService;
     let useEnvExtensionStub: sinon.SinonStub;
+    let pythonConfig: TypeMoq.IMock<WorkspaceConfiguration>;
     const progressOptions = {
         location: ProgressLocation.Window,
         title: Interpreters.activatingTerminals,
@@ -122,6 +125,8 @@ suite('Terminal Environment Variable Collection Service', () => {
             instance(shellIntegrationService),
             instance(envVarProvider),
         );
+        pythonConfig = TypeMoq.Mock.ofType<WorkspaceConfiguration>();
+        pythonConfig.setup((p) => p.get('terminal.shellIntegration.enabled')).returns(() => false);
     });
 
     teardown(() => {