switch to named, number-based types for units in all text/labeling related interfaces

[cgcostume]

similar to tuples.ts types such as GLclampf (which mostly resolve to number or array of number) units could be encoded in all function signatures, making it easier to understand the code just by signature (even without comments). For now this seems most relevant for text features of webgl-operate. Especially labeling position allows for a multitude of units depending on the label type.