Move KeyValueDatabase to WordPressShared

[mokagio]

It's used by types that we need to move in WordPressData.

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Part of #24165

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	App Name	WordPress Alpha
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	Build Number	pr24196-f847881
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	Bundle ID	org.wordpress.alpha
	Commit	f847881
	App Center Build	WPiOS - One-Offs #11644

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📲 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	pr24196-f847881
	Version	25.8
	Bundle ID	com.jetpack.alpha
	Commit	f847881
	App Center Build	jetpack-installable-builds #10673

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[kean]

I hope you don't mind if I merge this – seems harmless and I need this change in one of my PRs.

[mokagio]

@kean

I hope you don't mind if I merge this – seems harmless and I need this change in one of my PRs.

Not at all. Glad my small extraction PRs are useful for your work, too. It's not surprising given we're both ripping stuff out, but it's still nice when someone can build on top of your work.