[Large] Create UI for metadata editing workflow

This PR creates the main part of the UI for editing file metadata from BFF based on the Figma designs. Does not include any backend logic.

Part of #96

Reviewing

Lots of changes with a slightly complicated file structure, so here's suggested review order:

Entrypoint: added edit to the dropdown menu in packages/core/hooks/useFileAccessContextMenu.ts
This opens the modal, which is packages/core/components/Modal/EditMetadata/index.tsx
The modal renders the actual editing component (packages/core/components/EditMetadata/index.tsx), which is a wrapper for both the "new" and "existing" annotation pathways
- Pathway for editing files' values for an existing annotation: packages/core/components/EditMetadata/ExistingAnnotationPathway.tsx
- Pathway for creating a new annotation on the files: packages/core/components/EditMetadata/NewAnnotationPathway.tsx
BOTH pathways then point at packages/core/components/EditMetadata/MetadataDetails.tsx, which displays the current values for the files and provides an input field to enter the desired replacement values

There's also a brand new 'ComboBox' component (dropdown selector with search), which is a styled wrapper for the FluentUI combo box

Unit tests
340 (date, number, yes/no, etc)
341
342 -- Ideally should open on click and react to users hitting enter, but has been behaving inconsistently
343 Add disabled annotations (e.g., from labkey) & prevent new annotations that collide with existing
344 Warn users on exit w/ unsaved changes