fix(clipboard): Android warnings and build on SDK under 28 (#1771)

plugins/clipboard-manager/android/src/main/java/ClipboardPlugin.kt

@@ -4,12 +4,12 @@
 
 package app.tauri.clipboard
 
-import android.R.attr.value
 import android.app.Activity
 import android.content.ClipData
 import android.content.ClipDescription
 import android.content.ClipboardManager
 import android.content.Context
+import android.os.Build
 import app.tauri.annotation.Command
 import app.tauri.annotation.InvokeArg
 import app.tauri.annotation.TauriPlugin
@@ -59,6 +59,9 @@ internal class ReadClipDataSerializer @JvmOverloads constructor(t: Class<ReadCli
 
         jgen.writeEndObject()
       }
+      else -> {
+        throw Exception("unimplemented ReadClipData")
+      }
     }
 
     jgen.writeEndObject()
@@ -93,7 +96,7 @@ class ClipboardPlugin(private val activity: Activity) : Plugin(activity) {
       is WriteOptions.PlainText -> {
         ClipData.newPlainText(args.label, args.text)
       } else -> {
-        invoke.reject("Invalid write options provided")
+        invoke.reject("unimplemented WriteOptions")
         return
       }
 
@@ -128,7 +131,11 @@ class ClipboardPlugin(private val activity: Activity) : Plugin(activity) {
   @Command
   fun clear(invoke: Invoke) {
       if (manager.hasPrimaryClip()) {
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.P) {
           manager.clearPrimaryClip()
+        } else {
+          manager.setPrimaryClip(ClipData.newPlainText("", ""))
+        }
       }
       invoke.resolve()
   }