NavTab: Support overwriting TextTransform

[noahwebs]

Is your feature request related to a problem? Please describe. When using Tabs and NavTabs, the text-transform is hardcoded to uppercase which goes against the style my UX team has prescribed for my use case.

Describe the solution you'd like In the same way that the Button component allows setting the textTransform through the ButtonTextTransform property, Tabs and NavTabs should support a TabTextTransform property.

Describe alternatives you've considered As a workaround, I can insert a styled span to overwrite the text-transform property, but this workaround is annoying to reimplement every time.