Fetch Gridicons via SwiftPM

[mokagio]

Fix

See https://linear.app/a8c/issue/AINFRA-445 and previous PRs like #1713 .

Test

Run the app on Simulator or device and check either the magic link flow or the privacy screen as they are the only ones using Gridicons. Notice the icons are still there

Note

UI tests failing because of #1717

Review

Only one developer required to review these changes, but anyone can perform the review.

Release

These changes do not require release notes.

[wpmobilebot]

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

	App Name	Simplenote Prototype Build
	Build Number	1289
	Version	PR #1714
	Bundle ID	com.codality.NotationalFlow.Alpha
	Commit	40f8106
	Installation URL	0ur5oikj8f55o

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