Fix scroll to note designs

What does this MR do?

• Make shouldScrollToDiscussion a component method (previously was, incorrectly, defined as a computed prop)
• Take all a discussions notes into account when determining if the active discussion should be highlighted and/or scrolled into view. This means that when a note that isn't the first note of a discussion is in the URL hash, the discussion will still get highlighted correctly, and activate the appropriate pin on the overlay

Related to #225987 (closed) and #244882 (closed)

Demo

Now, linking to any note within a discussion will result in that discussion being "active".

Note: demo out of date. Initially, if no active discussion, all pins will be in "active" state (not opaque)

Clicking first note of a discussion

Clicking first note of a discussion

Clicking last note of a discussion

Note: demo out of date. Initially, if no active discussion, all pins will be in "active" state (not opaque)

Clicking last note of a discussion

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team