Add maxTargetSdk restriction to IMM fields

CL[1] and CL[2] refined mCurId and mCurMethod into the
BindState, annotated them with deprecated.

This is a follow up change to add maxTargetSdk for these
UnsupportedAppUsage fields to be restricted android U.

[1]: I010bc0ad196492bfac244b756dcfd986b9075698
[2]: Ie29597118ab7f37d3f1ac2a5368b28f0462e7a0a

Bug: 236937383
Test: presubmit
Change-Id: I77859113768cb8545924e9e29473a20aa2f624c6

core/java/android/view/inputmethod/InputMethodManager.java

@@ -550,7 +550,10 @@ public final class InputMethodManager {
      */
     @Deprecated
     @GuardedBy("mH")
-    @UnsupportedAppUsage
+    @UnsupportedAppUsage(trackingBug = 236937383,
+            maxTargetSdk = Build.VERSION_CODES.UPSIDE_DOWN_CAKE,
+            publicAlternatives = "Apps should not change behavior based on the currently connected"
+                    + " IME. If absolutely needed, use {@link InputMethodInfo#getId()} instead.")
     String mCurId;
 
     /**
@@ -561,7 +564,9 @@ public final class InputMethodManager {
     @Deprecated
     @GuardedBy("mH")
     @Nullable
-    @UnsupportedAppUsage
+    @UnsupportedAppUsage(trackingBug = 236937383,
+            maxTargetSdk = Build.VERSION_CODES.UPSIDE_DOWN_CAKE,
+            publicAlternatives = "Use methods on {@link InputMethodManager} instead.")
     IInputMethodSession mCurMethod;
 
     /**