fix(kotlin): a private property, and the members of a private class, stay in their file

A Kotlin property was indexed without its visibility modifier, so the
Kotlin file-local rule (#1745), which declines a private fun in another
file, read every property as public: a call like token(...) could link
to another file's @Volatile private var token, and JavaScript, Go or
Python callers to a Kotlin test fixture's private val. A public member
of a private class or object was reachable from other files too, though
nothing outside its file can name it.

Both extractors (wasm and the native kernel) now read a property's
modifiers the way they read a function's, and a candidate inside a
private Kotlin class or object is declined from another file. That
second rule is Kotlin's alone: a Scala private[pkg] class, or one with
a private constructor, is its package's, and a C# private nested class
serves every file of its partial class. Applied to every language where
private is file-local, as the PR had it, it removed 742 edges on http4s
(right ones among them, like stream.receiveHeaders() on a private[h2]
class H2Stream), 91 on scalachess and 10 on serilog (9 of them right
typed edges).

Validation:
- cross-file-visibility.test.ts: 2 cases, red on main, green here; the
  kernel parity fixture gains a private val and an internal var.
- Kernel parity (kotlin), 0 diffs: okhttp 588/619 files, mihon 891/940,
  nowinandroid 340/350, SystemUI's Kotlin 188/198 byte-identical, the
  same files deferred to wasm as with main's kernel; torture 1/1.
- A/B against main 01e0ac3a (with the Kotlin receiver typing of #1933):
  okhttp -274, mihon -177, SystemUI -94, every one a call from another
  file onto a private Kotlin property or a member of a private class or
  object (okhttp's private inner AndroidQuery.enqueue and
  RealWebSocketTest's private TestStreams, mihon's private IntentFilter
  filter that collections' filter { } reached, SystemUI's private
  MyExecutor.execute); nothing added. nowinandroid, jextract, click and
  gin identical; against main 4eb8c2a5, http4s, scalachess and serilog
  were identical too.
- Cost (mihon, median of 3 interleaved indexes, on main 4eb8c2a5): CPU
  25.7 s on main vs 25.5 s, wall 8.2 s on both.

Original PR #1761 by @danusha2345.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

codegraph-kernel/src/kotlin.rs

@@ -806,9 +806,11 @@ impl<'t> Walker<'t> {
             return Some(Vec::new());
         };
         // The `type`-field signature read is dead (zero fields) → signature
-        // undefined; NO docstring/visibility/isStatic — the modifiers merge in
-        // create_node still decorates expect/actual properties.
-        let row = self.create_node(kind, &name, node, Extra::default());
+        // undefined; NO docstring/isStatic — the modifiers merge in
+        // create_node still decorates expect/actual properties. Visibility IS
+        // read: a `private val` is file-local to the resolver (#1731).
+        let extra = Extra { visibility: Some(self.visibility_of(node)), ..Extra::default() };
+        let row = self.create_node(kind, &name, node, extra);
         // Walk the initializer ATTRIBUTED to the declared symbol (#693, the Go
         // fix, ported): without this the subtree is only fn-ref-scanned, so a
         // lambda / SAM / object initializer (`val cb = Runnable { target() }` —