Swatches: swatch.library.copyToUser copies a loaded library into User Defined

swatch.library.copyToUser {library} copies a library loaded from
another folder into the user library folder of the desktop app. A
.vcswatches, .gpl or .ase file is copied as it is; the swatches of a
document and a library loaded from the data or dataBase64 parameter are
written as a .vcswatches file. The copy gets a name that no file in the
folder has, and when a file with the same extension and bytes is
already there, that file is used. The library is then listed as User
Defined only. Until the app quits, commands given its loaded id use the
copy, unless another library is loaded under that id. Without a user
library folder (the web and headless sessions) the command is disabled.

A file with the same extension and bytes as a User Defined library
opens as that User Defined library. The unchanged original of a copied
.ase file is one such file. Graphic style libraries open the same way.

docs/control-protocol.md

@@ -154,7 +154,8 @@ Clicking a swatch there runs `swatch.library.add {library, names: [name], apply}
 one with Alt), so one undo step adds and applies it; Shift/Cmd-clicks select swatches and colour groups for
 Add to Swatches.
 `window.swatchLibrary.other {path?}` loads a library file (or another document's swatches) and opens it there;
-opening a `.vcswatches`, `.gpl` or `.ase` file with `app.open` does the same. `ui.saveSwatchLibrary {names?}` opens the
+opening a `.vcswatches`, `.gpl` or `.ase` file with `app.open` does the same. A file with the same extension and
+bytes as a User Defined library opens as that library. `ui.saveSwatchLibrary {names?}` opens the
 `saveSwatchLibrary` dialog (fields `name`, `format`: `vcswatches`/`gpl`/`ase`/`css`, `user`: save to the user library
 folder, `selectedOnly` with `names`); `ui.dialog.confirm` runs `swatch.library.save` (to a file it asks for a path
 and suggests `name` with the format's extension as the file name; the web downloads the file under that name).