Add view only state to filtered search input and tokens

What does this MR do?

Add a view-only property to all filtered search components. When set it true a user can only view the token values and editing is disabled.

The following changes are made:

1. Adds a viewOnly prop to filtered_search.vue. When true:
   • Disables gl-search-box-by-click.
   • Prevents an empty token from being appended.
   • Adds styling that matches a readonly form input.
   • Propagates down to the other token components.
2. Adds a viewOnly prop to filtered_search_token.vue. When true:
   • Prevents any actions.
   • Overrides the pointer cursor.
   • Does not apply a mouse EH.
   • Sets viewOnly: true on the GlToken.
3. Adds a viewOnly prop to filtered_search_token_segment.vue. When true:
   • Overrides the pointer cursor.
   • Does not apply a mouse EH.
4. Adds a viewOnly prop to filtered_search_term.vue. When true:
   • Sets the input to readonly.
   • Applies readonly style to the input that matches form input.

Related issue

GlFilteredSearch - Add readonly state to search... (#1699 - closed)

Screenshots

View only

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines.
• GitLab UI's contributing guidlines.
• 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 in the following projects to ensure that the @gitlab/ui package can be upgraded quickly after the changes are released:
  • GitLab: mr_url
  • CustomersDot: mr_url
  • Status Page: mr_url
• 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.

Closes #1699 (closed)