handle trailing slash with engines (test case for #7842)

Add test to avoid regression of 58e48d52

[ci skip]

Add app Rake tasks when -T and --dummy-path is passed to `plugin new`

Closes #8121

The `plugin new` generator always adds the dummy app rake tasks,
when a dummy app was created.

This is already handled by #find, it's a duplicate check, since
find_with_ids is not called from anywhere else.

Commit 65a2977c has introduced some
changes to format content for small devices, this change reverts the
original font size for normal screens while maintaing the same format
for these devices.

[ci skip]

[ci skip]

Permitted should be sticky on #slice

use Array() instead of flatten

* move ActiveModel::Errors tests to errors_test.rb
* add spec coverage for add_on_empty and add_on_blank

Fix some indenting for some properties and closing }, remove tabs, and
merge two pre/code definitions.

[ci skip]

Current stable guides show the "Guides Index" links without underline,
just showing it when it's hovered. This restores the same functionality
for edge guides.

Also remove annoying pointer cursor while accessing guides index,
restoring previously functionality: now the pointer cursor only appears
when hovering a link.

Closes #8107 [ci skip]

ArgumentError is better suited than RuntimeError for this.

Use `tag!` instead of `method_missing` in `to_xml` conversions.

Since version `3.0.x` `Builder` caches method passed to `method_missing` each time. This commit replaces `method_missing` call with `tag!` call to prevent method redefinition on each `to_xml` call with the same builder.