Refactor Util's Product API to use enum instead of String keys

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: None
• Fix Version/s: alloy-2.0.0, alloy-3.0.0, portal-3.0.0, util-1.0.0, util-2.0.0, util-3.0.0, bridge-impl-2.0.0, bridge-impl-3.0.0, metal-1.0.0, bridge-ext-1.0.0, bridge-ext-2.0.0, bridge-ext-3.0.0, bridge-ext-5.0.0, showcase-2.0.0, bridge-impl-4.0.0, bridge-impl-5.0.0, showcase-3.0.0, bridge-ext-6.0.0
• Component/s: JSF Showcase, Liferay Faces Alloy / Showcase / Tests, Liferay Faces Bridge Ext, Liferay Faces Bridge Impl / Demos / Tests, Liferay Faces Metal / Showcase / Tests, Liferay Faces Portal / Demos / Tests, Liferay Faces Util
• Labels: None

{markdown}
This task involves changing `ProductConstants` to a `enum`. The `enum` should be called `Name` and should be moved into the `Product` interface. Changing to an `enum` will help us to avoid pitfalls with changing String constant values. [Changing String constant values seems like an implementation detail but is actually a breaking API change due to the fact that Java compilation inlines String constants during compilation.](https://web.liferay.com/community/forums/-/message_boards/message/32606100#_19_message_32621317){markdown}

This improvement and the improvement for FACES-2753 can be made at the same time.