Support hovering limits for adts
Fix#17009
1. Currently, r-a supports limiting the number of struct fields displayed when hovering. This PR extends it to support enum variants and union fields. Since the display of these three (ADTs) is similar, this PR extends 'hover_show_structFields' to 'hover_show_adtFieldsOrVariants'.
2. This PR also resolved the problem that the layout of ADT was not restricted by display limitations when hovering on the Self type.
3. Additionally, this PR changes the default value of display limitations to `10` (instead of the original `null`), which helps users discover this feature.
