Replace PlusCircleIcon with RhUAddCircleFillIcon

[nicolethoen]

Summary

Replace all usages of the legacy FA PlusCircleIcon with the RH brand RhUAddCircleFillIcon.

Linked PR

• chore(PlusCircleIcon): Replace all usages of PlusCircleIcon with RhUAddCircleFillIcon #12369

Acceptance Criteria

• All PlusCircleIcon imports replaced with RhUAddCircleFillIcon

• No broken links or references as a result of the change

• Tests pass

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Jira Issue: PF-4086

[coderabbitai]

🔗 Related PRs

#12366 - chore(ExternalLinkSquareAltIcon): Replace all usages of ExternalLinkSquareAltIcon with RhUiExternalLinkFillIcon [merged]
#12371 - chore(Star Icons): Replace all star FA icons with RH brand star icons [merged]
#12376 - chore(EmptyState): Update use a RH brand icon in tests [merged]
#12379 - chore(OutlinedQuestionCircleIcon): Update uses of OutlinedQuestionCircleIcon to use RhUiQuestionMarkCircleIcon [merged]
#12387 - feat: update rhds icons to 2.2.0 [merged]

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