Contributes to https://gitlab.com/gitlab-org/gitlab/-/issues/358703

**Problem**

Code that ends with a `do` block definition is ignored by parser. The
linter can skip some of broken links because of that.

**Solution**

Add a workaround for this case.

Contributes to https://gitlab.com/gitlab-org/gitlab/-/issues/328203

**Problem**

NodePattern#match returns the first matching subnode and ignores other
matches

**Solution**

Apply NodePattern#match for all node descendants

Related issue: https://gitlab.com/gitlab-org/gitlab/-/issues/208354
Previou implementation MR:
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/35351

**Problem**

The documentation link linter checks links defined by `help_page_path`
helper, however it ignores links from `help_page_url`.

**Solution**

Extend the pattern to match both `help_page_path` and `help_page_url`
helper methods

Issue: https://gitlab.com/gitlab-org/gitlab/-/issues/218764
Follow-up for:
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/39717
After merging:
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/39715

* Revert an approximate match in the documentation linter
* Revert an allow_failure: true behavior
* Update a regular expression to remove false-positives in the linter

Contributes to https://gitlab.com/gitlab-org/gitlab/-/issues/208354

We want to validate if there are any broken links and dead anchors to
documentation pages.

Extra:
* Extract anchor generation logic into Gitlab::Utils::Markdown module

The plan for RSpec 4.0 is to disable monkey patching, reference:
https://rspec.info/blog/2013/07/the-plan-for-rspec-3/#zero-monkey-patching-mode
https://relishapp.com/rspec/rspec-core/docs/configuration/zero-monkey-patching-mode

This commit stops using RSpec monkey patching in several specs.

Files in lib will be eager loaded and hence will require haml_lint to be
loaded. Since this is only a development dependency, we can't assume
this gem will be available in production, so it should never be loaded
in production.