Combine file and symbol data into a single panel

Created by: benvenker

• Nest symbols under files
• Utilize hierarchy for within symbols if possible we'll deal with hierarchy of the symbols later

Instead of using icons for identifying symbols, use text tags (full list here). We should use the same background color for the tags as their icons use, but replace the icons with these.

Example Figma here.

• cc @novoselrok for #38810 (closed)

Sourcegraph:

GitHub: