ffi #jni_main: emit name: Type; body members as private Java fields

`#jni_class` body items of the form `name: Type;` were parsed into
`ForeignFieldDecl` but dropped by jni_java_emit. They now render as
private Java fields between the static init block and the @Override
delegates, using the same primitive / `*Foo` → fully-qualified-name
type mapping as method parameters.

Needed for the chess-on-Pixel `SxApp` Activity to hold its
`SurfaceView` reference: `view: SurfaceView;` → `private
android.view.SurfaceView view;`.

src/ir/jni_java_emit.zig

@@ -125,6 +125,20 @@ pub fn emitJavaSource(
         try buf.appendSlice(allocator, "\"); }\n");
     }
 
+    // Fields. `name: Type;` body items render as private Java fields —
+    // primitive types pass through, pointer types resolve to fully
+    // qualified Java class names via the class registry.
+    for (fcd.members) |m| switch (m) {
+        .field => |fd| {
+            try buf.appendSlice(allocator, "    private ");
+            try emitJavaType(allocator, &buf, fd.field_type, opts);
+            try buf.append(allocator, ' ');
+            try buf.appendSlice(allocator, fd.name);
+            try buf.appendSlice(allocator, ";\n");
+        },
+        else => {},
+    };
+
     // Two passes: @Override stubs + native delegate; then the native
     // declarations.
     for (fcd.members) |m| switch (m) {