SelectableText → ScrollTextCore; EditField → EditBoxCore

[dhardy]

Since SelectableText and EditField do not have scroll support they are best not used except as a child of another widget which manages their scroll behaviour (i.e. ScrollText, EditBox). The renames help emphasize this. (Further renaming before the next release is possible; internal module edit_field is not renamed for now.)

The property editable is replaced with read_only (an inversion: slightly clearer and aligns the default behaviour with the default boolean value false).

Add fn EditBox::with_frame_style; use in examples/splitter.rs instead of EditField. Motivation: EditField should not have been used here since it does not support scrolling. This is somewhat of a hack; ideally frames and margins will be reworked to avoid drawing "box" boundaries next to a visual divider like GripPart.

[m-hugo]

Since SelectableText and EditField do not have scroll support they are best not used except as a child of another widget which manages their scroll behaviour (i.e. ScrollText, EditBox). The renames help emphasize this.

Since SelectableText does not have scroll support, let's rename it ScrollTextSomething lol

and what if someone is looking for selectable non-scrolling text or scrolling non-selectable text?