feat: switched chat to GlDuoChat component

Description

This is the integration branch for the shared GlDuoChat component in the VSCode extension. The new component replaces the custom implementation of chat with the unified GlDuoChat component.

This is an action similar to Swapped AIGenieChat with DuoChat component (gitlab!134669 - merged) in the main GitLab project.

Related Issues

By bringing the shared GlDuoChat component into the extension, this MR closes several MRs at the same time:

• Add the new GitLab Duo chat package as a Vue2 e... (#996 - closed),
• Customize the look of the chat to work with the... (#997 - closed),
• Update BE-FE communication signatures to match ... (#995 - closed),
• Setup the communication layer between BE and th... (#998 - closed)
• Support the SVG icons in WebView, incl. the inl... (#1068 - closed)
• Add an empty state for first time use (gitlab#421397 - closed)
• Add prompts on IDE chat (gitlab#421417 - closed)
• Update loading state in IDE chat (gitlab#421400 - closed)

How has this been tested?

The change has been tested in the desktop VSCode 1.84.0

Screenshots (if appropriate):

State	Screenshot
Empty state
Loading state
Documentation question/answer
Code-related question/answer
User feedback form
User feedback form in a wider panel

Visual themes adaptability

Dark themes	Light Themes

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation
• Chore (Related to CI or Packaging to platforms)
• Test gap

Related to #996 (closed)