Fixed issue with setting unwanted disallowed styles by image dialog.
Code refactoring: Wrapped image plugin test in IIFE and added strict mode.
Tests: added for #12132.
Tests: Set editors to inline mode in image plugin tests.
Tests: Test stopped working after changing editors to inline mode, because wrong image was checked.
Tests: Added test for image dialog automatically loading image's dimensions.
Changelog entry and corrections.
Merge branch 't/12132'