Remove connection string validation for connection string login

- Remove validateDirectConnectionStringLogin and its helpers (extractEndpointHostFromConnectionString, extractHostToken, directLoginAllowlistedEndpointZones)
- Remove old extractMasterKeyfromConnectionString (Gremlin-specific), rename extractAccountKeyFromConnectionString to extractMasterKeyfromConnectionString
- Change validateDirectConnectionStringConnectivity to throw on error instead of returning string|undefined
- Simplify direct-login flow: submit connection string to CosmosClient as-is, no format or endpoint validation
- Keep connectivity pre-check (throws if CosmosClient cannot reach account)
- Remove 6 unused localization keys for validation errors
- Update tests to match new behavior

src/HostedExplorer.test.tsx

@@ -159,7 +159,7 @@ describe("HostedExplorer tryCosmosDB postMessage handler", () => {
   });
 
   it("does not open the Data Explorer when the Cosmos client cannot connect", async () => {
-    mockValidateDirectConnectionStringConnectivity.mockResolvedValue("Unable to connect to the account.");
+    mockValidateDirectConnectionStringConnectivity.mockRejectedValue(new Error("Unable to connect to the account."));
     const { container } = render(<App />);
 
     const validConnStr = `AccountEndpoint=https://${FAKE_ACCOUNT_NAME}.documents.azure.com:443/;AccountKey=${FAKE_KEY};`;