AW: prefer androidx annotations

No change to logic.

This swaps android.support.annotation.* for androidx.annotation.* in
//android_webview/. Both of these are @Retention(SOURCE), so they'll
have no effect on the product's behavior.

No BUILD file changes because we were depending on android.support.*
transitively (which was a bug we've now fixed) and already depended on
androidx.annotation.* (so now our folder is consistent).

Test: N/A
Change-Id: I9cb65d5eb2cc0d52f56403d804b0b4f6b4acf49d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1842614
Auto-Submit: Nate Fischer <ntfschr@chromium.org>
Reviewed-by: Tao Bai <michaelbai@chromium.org>
Commit-Queue: Nate Fischer <ntfschr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#703124}

android_webview/java/src/org/chromium/android_webview/WebMessageListenerHolder.java

@@ -5,7 +5,8 @@
 package org.chromium.android_webview;
 
 import android.net.Uri;
-import android.support.annotation.NonNull;
+
+import androidx.annotation.NonNull;
 
 import org.chromium.base.annotations.CalledByNative;
 import org.chromium.base.annotations.JNINamespace;