language: Make Buffer::new take an explicit ID (#2900)

See Linear description for the full explanation of the issue. This PR is
mostly a mechanical change, except for the one case where we do pass in
an explicit `next_id` instead of `model_id` in project.rs.

Release Notes:
- Fixed a bug where some results were not reported in project search in
presence of unnamed buffers.

crates/language/src/buffer.rs

@@ -347,13 +347,9 @@ impl CharKind {
 }
 
 impl Buffer {
-    pub fn new<T: Into<String>>(
-        replica_id: ReplicaId,
-        base_text: T,
-        cx: &mut ModelContext<Self>,
-    ) -> Self {
+    pub fn new<T: Into<String>>(replica_id: ReplicaId, id: u64, base_text: T) -> Self {
         Self::build(
-            TextBuffer::new(replica_id, cx.model_id() as u64, base_text.into()),
+            TextBuffer::new(replica_id, id, base_text.into()),
             None,
             None,
         )