ffi 1.21: #jni_call(bool) → CallBooleanMethod (slot 37) — make-green

One-line addition: `.bool => Jni.CallBooleanMethod`. The lazy-cache
+ dispatch from 1.17 handles the rest. JNI's `jboolean` is i8 in the
C ABI but always carries 0 or 1; LLVM's call boundary truncates the
return byte to i1 and the sx-level bool reads the low bit
canonically.

IR snapshot updated: `ret i1 undef` replaced by the full sequence
through vtable slot 37 keyed on `("isShown", "()Z")`.

src/ir/emit_llvm.zig

@@ -1244,6 +1244,7 @@ pub const LLVMEmitter = struct {
                     .s32 => Jni.CallIntMethod,
                     .s64 => Jni.CallLongMethod,
                     .f64 => Jni.CallDoubleMethod,
+                    .bool => Jni.CallBooleanMethod,
                     else => {
                         self.mapRef(c.LLVMGetUndef(self.toLLVMType(instruction.ty)));
                         return;