fix(GlPopover): Pass through popover manual events

What does this MR do?

BootstrapVue Popover component allows to programmatically open, close, disable, and enable popovers by triggering events. GitLab UI tooltip component, which is a simple wrapper around BVPopover, can’t do the same because when emitting an event that manually changes the state of the popover, for example:

<script>
export default {
  methods: {
    hide() {
      this.$refs.glPopover.$emit('hide');
    }
  }
}
</script>

the event is emitted in the wrapper but the underlying BVPopover instance does not catch this event. This Merge Request fixes this problem by passing through the emitted event to the BVPopover instance. A similar problem was fixed in !1711 (merged) for tooltips.

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.