Return early in activate from env var collection (microsoft#25286)

Resolves: microsoft#25275
microsoft#25284
It seems like python env var experiment is interfering when env
extension is being used.
We should not implicit activate with env var experiment if environment
extension is installed and being used.

---------

Co-authored-by: Eleanor Boyd <[email protected]>

Author: anthonykim1

src/client/terminals/envCollectionActivation/service.ts

@@ -97,6 +97,14 @@ export class TerminalEnvVarCollectionService implements IExtensionActivationServ
 
     public async activate(resource: Resource): Promise<void> {
         try {
+            if (useEnvExtension()) {
+                traceVerbose('Ignoring environment variable experiment since env extension is being used');
+                this.context.environmentVariableCollection.clear();
+                // Needed for shell integration
+                await registerPythonStartup(this.context);
+                return;
+            }
+
             if (!inTerminalEnvVarExperiment(this.experimentService)) {
                 this.context.environmentVariableCollection.clear();
                 await this.handleMicroVenv(resource);