[Core] Polish pass on struct member names

[farism]

Suggestions for some member renames, mostly to reduce redundancies. This should help make the UI code a bit more terse. While there is value in having the names be fully descriptive, I believe once you learn the concepts that value quickly diminishes. Therefore the readability of the UI code is paramount.

Clay_TextElementConfig.fontId -> Clay_TextElementConfig.font
Clay_TextElementConfig.fontSize -> Clay_TextElementConfig.size
Clay_TextElementConfig.textColor -> Clay_TextElementConfig.color

Clay_ScrollContainerData.scrollContainerDimensions -> Clay_ScrollContainerData.containerDimensions

Clay_LayoutConfig.childGap -> Clay_LayoutConfig.gap
Clay_LayoutConfig.childAlignment -> Clay_LayoutConfig.alignment
Clay_LayoutConfig.layoutDirection -> Clay_LayoutConfig.direction

[nicbarker]

Thanks for opening this, especially the text element config changes are a great idea. Will get them in after #240 merges.