feat: Enable sharing to non-Jetpack sites

[dcalhoun]

The Jetpack app is no longer positioned to be a product focused solely on Jetpack sites. Therefore, when sharing content to the Jetpack app, we should allow sharing content to non-Jetpack sites.

Filtering the Jetpack app to include only Jetpack sites was done intentionally in #16140. The filtering was reverted in #17914, but the changes overlooked the sharing extension.

Fixes #23707.

To test: Perform the steps outlined in #23707.

Regression Notes

1. Potential unintended areas of impact
   Sharing features.
2. What I did to test those areas of impact (or what existing automated tests I relied on)
   Manually tested sharing content to the Jetpack app.
3. What automated tests I added (or what prevented me from doing so)
   Deemed it unnecessary for this small change reverting a previously intentional
   change.

PR submission checklist:

• I have completed the Regression Notes.
• I have considered adding unit tests for my changes.
• 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.

Testing checklist:

• WordPress.com sites and self-hosted Jetpack sites.
• Portrait and landscape orientations.
• Light and dark modes.
• Fonts: Larger, smaller and bold text.
• High contrast.
• VoiceOver.
• Languages with large words or with letters/accents not frequently used in English.
• Right-to-left languages. (Even if translation isn’t complete, formatting should still respect the right-to-left layout)
• iPhone and iPad.
• Multi-tasking: Split view and Slide over. (iPad)

[dangermattic]

	1 Warning
⚠️	PR is not assigned to a milestone.

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[wpmobilebot]

📲 You can test the changes from this Pull Request in WordPress Alpha by scanning the QR code below to install the corresponding build.

	App Name	WordPress Alpha
	Configuration	Release-Alpha
	Build Number	pr23778-e1a3980
	Version	25.4.2
	Bundle ID	org.wordpress.alpha
	Commit	e1a3980
	App Center Build	WPiOS - One-Offs #11005

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[wpmobilebot]

📲 You can test the changes from this Pull Request in Jetpack Alpha by scanning the QR code below to install the corresponding build.

	App Name	Jetpack Alpha
	Configuration	Release-Alpha
	Build Number	pr23778-e1a3980
	Version	25.4.2
	Bundle ID	com.jetpack.alpha
	Commit	e1a3980
	App Center Build	jetpack-installable-builds #10045

Automatticians: You can use our internal self-serve MC tool to give yourself access to App Center if needed.

[kean]

I tested the changes, and they work as expected. Great catch – one less paper cut.

I'm still not sure under what circumstances you'd want to see only self-hosted sites connected to Jetpack but not the wp.com sites, but that's now irrelevant.