Fix stats widget not loading stats activity correctly

[mkevins]

Fixes #16637

This PR sets the pending intent template with FLAG_MUTABLE. This is necessary in order for widget subview click-handlers to be differentiated. This should be ok to mark mutable since this is an explicit intent.

To test:

Follow the steps in #16637 and the stats activity should open normally when tapping either the title or subviews of the stats widget.

Regression Notes

1. Potential unintended areas of impact
   N/A

2. What I did to test those areas of impact (or what existing automated tests I relied on)
   Manual testing

3. What automated tests I added (or what prevented me from doing so)
   This is out of scope for this fix.

PR submission checklist:

• I have completed the Regression Notes.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[wpmobilebot]

📲 You can test these changes on WordPress by downloading wordpress-installable-build-pr17439-a810f9e.apk

	💡 Scan this QR code with your Android phone to download and install the APK directly on it.
	App	WordPress
	Build Flavor	Jalapeno
	Build Type	Debug
	Commit	a810f9e

Note: This installable build uses the JalapenoDebug build flavor, and does not support Google Login.

[wpmobilebot]

📲 You can test these changes on Jetpack by downloading jetpack-installable-build-pr17439-a810f9e.apk

	💡 Scan this QR code with your Android phone to download and install the APK directly on it.
	App	Jetpack
	Build Flavor	Jalapeno
	Build Type	Debug
	Commit	a810f9e

Note: This installable build uses the JalapenoDebug build flavor, and does not support Google Login.

[ravishanker]

Thanks for taking care of this 🚀

[mkevins]

Thank you for reviewing 👍