Tests: Removing and restoring filling char on image creation.
Store the anchor offset so it can be precisely restored when restoring the filling char.
Tests: Tests for #8617 and #12491.
Store anchor and focus nodes, because they may be changed when chaning filling node's text.
Extracted repeating fragments of tests.
Tests: Added test for keeping selection direction when removing filling char.
Keep selection's direction when removing filling char.
Tests: Test for preserving selection's direction when taking snapshot.
Preserve selection's direction when taking snapshot.
Changelog entry.
Merge branch 't/12491'