Remove another unnecessary dup

Conflicts:
	activerecord/lib/active_record/dynamic_matchers.rb

do not append a second slash when using `trailing_slash: true`

Fix a number of validation/style errors

 * <pre> is not allowed to be nested inside of <p> elements in HTML
 * Indentation of </p> doesn't match corresponding <p>
 * <p> element not explicitly closed
 * One more </div> than <div>

In each case, the template was fixed to match how a HTML5 parser would "see"
the resulting page.

Remove unnecessary #dup

Allow toggling dumps on error page

Replace #flatten with Array()

Cleanup the CSS on the new error page.

refactoring to_sym of Symbol in preload

Add source code left padding on error pages

This is version of #8640 for master

Add missing changelog entry for #8676 [ci skip]

remove meaningless AS::FrozenObjectError

Address a failure test_remove_column_with_multi_column_index with Oracle

Not only PostgreSQL, Oracle database adapter drops the multi-column index
if any of the indexed columns dropped by remove_column.

unused scope in AR test model

Add -B alias for --skip-bundle