[iOS] Fix for TextDecorations not updating after modifying Label text

[Tamilarasan-Paranthaman]

Root Cause of the issue

When setting normal text dynamically, the previously set attributed text decoration remains. When trying to set new attributed text decoration, both the previously set and newly set attributed text decoration appear in the label.

Description of Change

When updating normal text, make sure that AttributedText is set to null to remove any decorations from previous updates. This ensures that the newly set attributed text works correctly.

Issues Fixed

Fixes #16967

Tested the behaviour in the following platforms

• [x] Android
• [x] Windows
• [x] iOS
• [x] Mac

Screenshot

Before Issue Fix	After Issue Fix

[dotnet-policy-service[bot]]

Hey there @Tamilarasan-Paranthaman! Thank you so much for your PR! Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[jsuarezruiz]

/azp run

[azure-pipelines[bot]]

Azure Pipelines successfully started running 3 pipeline(s).

[Tamilarasan-Paranthaman]

/rebase

[jsuarezruiz]

/rebase

[PureWeen]

/azp run

[azure-pipelines[bot]]

Azure Pipelines successfully started running 3 pipeline(s).