[9.5] Disallow the `name` attribute on all user-provided markup

See merge request gitlab/gitlabhq!2166

[9.5] Limit `style` attribute on `th` and `td` elements to specific properties

See merge request gitlab/gitlabhq!2155

Remove class from SanitizationFilter whitelist

See merge request !2079

Also adds details/summary tags to Copy-as-GFM

Closes #22911

The previous fix introduced another leak; as it made
Banzai::Filter::SanitizationFiler#customized? always return false, so we
were always appending two elements to
HTML::Pipeline::SanitizationFilter::WHITELIST[:elements]. This growth in
the elements array would slow the sanitization process over time.

This reverts commit 504a3b5e.

In Banzai::Filter::SanitizationFilter#customize_whitelist, we append
three lambdas that has reference to the SanitizationFilter instance,
which in turn (potentially) has a reference to the following chain:

context hash -> Project instance -> Repository instance -> lookup hash
-> various Rugged instances -> various mmap-ed git pack files.

All of the above is not garbage collected because the array we append
the lambdas to is the constant
HTML::Pipeline::SanitizationFilter::WHITELIST.

This reverts commit 3e991230.

# Conflicts:
#	app/models/project.rb

Closes #1625

We're trying to avoid circular dependency errors.

This prevents false matches on relative links like
`[database](database.md)`.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/14220

Closes https://dev.gitlab.org/gitlab/gitlabhq/issues/2660

Closes #13625

This allows for future pipelines to more easily define a custom
whitelist.

Closes #12517

Addresses internal https://dev.gitlab.org/gitlab/gitlabhq/issues/2613

When this option is `:description`, we use a more restrictive whitelist.
This is used for Project and Group description fields.

Fixes #1651

This just extends the HTML::Pipeline::SanitizationFilter with our custom
whitelist.