Fix missed renames in #22632 (#23688)

Fix a bug where a GPUI macro still used `ModelContext`
Rename `AsyncAppContext` -> `AsyncApp`
Rename update_model, read_model, insert_model, and reserve_model to
update_entity, read_entity, insert_entity, and reserve_entity

Release Notes:

- N/A

crates/gpui_macros/Cargo.toml

@@ -17,3 +17,6 @@ doctest = false
 proc-macro2 = "1.0.66"
 quote = "1.0.9"
 syn = { version = "1.0.72", features = ["full", "extra-traits"] }
+
+[dev-dependencies]
+gpui.workspace = true