[WIP] Cache granularity

tests/test-dirs/server-tests/typer-cache/granularity.t/run.t

@@ -0,0 +1,37 @@
+
+
+  $ $MERLIN server stop-server
+
+Let's start with populating typer cache
+  $ echo "let x = 1 \
+    \
+    module M = struct \
+    let y = 2 \
+    let z = 3 \
+    end" > before.ml
+
+  $ $MERLIN server errors -filename test.ml < before.ml
+  {
+    "class": "return",
+    "value": [],
+    "notifications": []
+  }
+
+TODO: After change inside module, Merlin should reuse items that are in module's prefix.
+  $ echo "let x = 1 \
+    \
+    module M = struct \
+    let y = 2 \
+    let a = 4 \
+    let z = 3 \
+    end" > after.ml
+
+  $ $MERLIN server errors -filename test.ml < after.ml \
+  > -log-section Mtyper -log-file - 2>&1
+  # 0.01 Mtyper - compatible_prefix
+  reusing 1 items, 1 new items to type
+  {
+    "class": "return",
+    "value": [],
+    "notifications": []
+  }