Fix crash in additionalTokenRefreshParameters when emmSupport is nil

[AkshatG6]

Overview
This PR fixes an edge case missed by the previous fix for the Swift casting crash in additionalTokenRefreshParameters (#564).

The Problem
The previous fix correctly converted non-string values (like NSNumber) into their NSString representations to avoid a Swift type mismatch exception. However, it missed the scenario where emmSupport is nil or NO. In that case, [GIDEMMSupport parametersWithParameters:emmSupport:isPasscodeInfoRequired:] returned the original parameters dictionary early, bypassing the newly added string conversion helper.

The Fix
This change updates the early return block to apply [GIDEMMSupport dictionaryWithStringValuesFromDictionary:parameters], ensuring that the dictionary is safely stringified regardless of the emmSupport configuration.

[w-goog]

Requested test changes :)

[w-goog]

This is good to merge :) You can override the swift integration test to do so. Before merging, please file a follow-up issue to make the following changes:

1. That the parametersWithParameters function drops key parameters that contain values like a nested array.
2. We should fix the test swizzling UIDevice to Not Do That (or ensure all the tests are doing it the same way; using the real UIDevice will be non-hermetic).
3. Consider upleveling these tests to the public API.

[AkshatG6]

Merging this PR.

1. Created Refactor and improve GIDEMMSupport parameters and tests #611 to track the requested GIDEMMSupport refactoring, UIDevice swizzling fixes, and upleveling of the unit tests.

2. As discussed, I am overriding the failing Swift integration test to merge this PR. The failure is due to the iOS 18 simulators breaking the hardcoded XCUITest scripts, which will be fixed in a follow-up PR.