Closes EP-193

Edit prediction context collection previously reused the editor
goto-definition / goto-type-definition path, which resolves every LSP
result into a `LocationLink` — opening a buffer per target (worktree
creation, buffer registration, anchor conversion) before edit prediction
gets a chance to filter. On remote projects the host additionally
created a peer-visible buffer per link and the client waited on each
one.

This adds a bespoke request path that returns raw results first and only
does the expensive work for results that survive filtering:

- New `EditPredictionDefinition { path: ProjectPath, range:
Range<Unclipped<PointUtf16>> }` boundary type. LSP wire types never
leave `lsp_command.rs`; the workspace-only filter and URI→`ProjectPath`
resolution happen while normalizing the LSP response, before any buffer
exists, so the type encodes the workspace-only invariant.
- New `GetEditPredictionDefinitions` /
`GetEditPredictionTypeDefinitions` LSP commands and proto messages.
Responses carry only path + UTF-16 range — the host never calls
`create_buffer_for_peer` and the client never waits on remote buffers.
- One public API: `Project::edit_prediction_definitions(buffer,
position, include_type_definitions, cx)` fires both LSP requests
concurrently and returns a merged, deduped list ("not capable" = empty).
The definition/type-definition split was never used downstream, so
`CacheEntry` now holds a single list and the fetch pipeline runs one
task per identifier.
- `edit_prediction_context` dedupes raw results before opening buffers;
survivors open via `project.open_buffer(ProjectPath)` (skipping the
invisible-worktree/yarn machinery of `open_local_buffer_via_lsp`, and
working identically on remote projects), then clip → anchor →
`MAX_TARGET_LEN`.
- Removes the `workspace_only` flag from `GetDefinitions` /
`GetTypeDefinitions`: edit prediction was its only user. The editor path
always sent `false`, which proto3 doesn't encode, so normal
goto-definition requests are wire-identical; old peers still sending
`true` get unfiltered results (graceful degradation). The proto field
numbers are `reserved`.

Tested with a local test proving filtering precedes buffer opening (an
out-of-workspace target never spawns a worktree, an oversized target is
excluded from related files) and a collab test proving the remote
round-trip returns correct paths/ranges without opening buffers on the
client.

Release Notes:

- N/A