fix R8 warning (#27291)

Summary:
R8 shows warning that **com.facebook.react.bridge.JavaScriptModule**, **com.facebook.react.bridge.NativeModule** are interfaces so proguard rules must use implements instead of extends. This PR changes proguard rules to fix the warnings.

## Changelog

[Android] [Changed] - Fix R8 warning
Pull Request resolved: #27291

Test Plan: RNTester builds and runs as expected.

Differential Revision: D18658704

Pulled By: mdvacca

fbshipit-source-id: a679643542bc55b89141f58c3236a29cf83c20d2

ReactAndroid/proguard-rules.pro

@@ -39,8 +39,8 @@
   *** get*();
 }
 
--keep class * extends com.facebook.react.bridge.JavaScriptModule { *; }
--keep class * extends com.facebook.react.bridge.NativeModule { *; }
+-keep class * implements com.facebook.react.bridge.JavaScriptModule { *; }
+-keep class * implements com.facebook.react.bridge.NativeModule { *; }
 -keepclassmembers,includedescriptorclasses class * { native <methods>; }
 -keepclassmembers class *  { @com.facebook.react.uimanager.annotations.ReactProp <methods>; }
 -keepclassmembers class *  { @com.facebook.react.uimanager.annotations.ReactPropGroup <methods>; }