plugins: add plugin typings for getRangeFontWeight

[Roystbeef]

https://github.com/figma/plugin-typings/pull/148 added types for fontWeight to StyledTextSegment but we also added getRangeFontWeight so adding types for this as well - implementation here: https://github.com/figma/figma/pull/74934

Test Plan

• assert that the types match those for the implementation