If resizable is TRUE, then the user can explicitly resize the column by
grabbing the outer edge of the column button. If resizable is TRUE and
sizing mode of the column is GTK_TREE_VIEW_COLUMN_AUTOSIZE, then the sizing
mode is changed to GTK_TREE_VIEW_COLUMN_GROW_ONLY.
If resizable is TRUE, then the user can explicitly resize the column by grabbing the outer edge of the column button. If resizable is TRUE and sizing mode of the column is GTK_TREE_VIEW_COLUMN_AUTOSIZE, then the sizing mode is changed to GTK_TREE_VIEW_COLUMN_GROW_ONLY.