feat(Alert): Use heading scale

What does this MR do?

We are trying to increase results, quality, and efficiency by using typography in a systematic way.

This MR updates popover to use the heading scale implemented in !3673 (merged).

gl-heading-scale-500 is used as the semantic heading scale does not visually align (see contextual adjustments).

Aligning the icon

Alerts contain an icon. This icon should be vertically centre aligned with the first line of text.

Previously, this was solved by having 2 values to position the icon. One for no title, and a slightly larger one when there is a title.

Our updated headings are dynamic, and change size based on the viewport width. Because of this we can't set a fixed offset from the top. This can make maintaining icon alignment with the first line of text tricky.

To enable this I have created gl-alert-icon-container. This container gets its height from an empty span with heights that match the type styles applied to the title and body. Allowing it to maintain alignment at any viewport width.

Spec

Design spec: https://www.figma.com/file/qEddyqCrI7kPSBjGmwkZzQ/%F0%9F%93%99-Component-library?type=design&node-id=95988-10021&mode=dev

For more context see:

• Type scale > Implement type scale specs (#2137)

Screenshots or screen recordings

Before	After
Kapture_2023-10-02_at_10.52.34	Kapture_2023-10-02_at_10.53.23

Integration merge requests

• GitLab: gitlab!133303 (closed)
• CustomersDot: mr_url
• Status Page: mr_url

Does this MR meet the acceptance criteria?

This checklist encourages the authors, reviewers, and maintainers of merge requests (MRs) to confirm changes were analyzed for conformity with the project's guidelines, security and accessibility.

Toggle the acceptance checklist

Conformity

• Code review guidelines.
• GitLab UI's contributing guidelines.
• If it changes a Pajamas-compliant component's look & feel, the MR has been reviewed by a UX designer.
• If it changes GitLab UI's documentation guidelines, the MR has been reviewed by a Technical Writer.
• If the MR changes a component's API, integration MR(s) have been opened (see integration merge requests above).
• Added the ~"component:*" label(s) if applicable.

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
• Security reports checked/validated by a reviewer from the AppSec team

Accessibility

If this MR adds or modifies a component, take a few moments to review the following:

• All actions and functionality can be done with a keyboard.
• Links, buttons, and controls have a visible focus state.
• All content is presented in text or with a text equivalent. For example, alt text for SVG, or aria-label for icons that have meaning or perform actions.
• Changes in a component’s state are announced by a screen reader. For example, changing aria-expanded="false" to aria-expanded="true" when an accordion is expanded.
• Color combinations have sufficient contrast.