Add data-engrid-highlight-required-fields style helper outside of flex2 theme

[StoneMoney]

Adds error_color * to end of required input label when body tag has data-engrid-highlight-required-fields

• Existed already for the flex2 layout, now expanded for all themes on an opt-in basis
• Marks the VGS fields as required when a card-based payment type is selected
• Does not apply to the give by select inputs

Demo page: https://fundraise.tpl.org/page/1000799/donate/1?mode=DEMO&assets=demo-req-asterisks