Resolve "Val cannot be reassigned" for primaryClip

"primaryClip" was converted to val after API 28.

Author: irfano

aztec/src/main/kotlin/org/wordpress/aztec/AztecText.kt

@@ -1926,8 +1926,8 @@ open class AztecText : AppCompatEditText, TextWatcher, UnknownHtmlSpan.OnUnknown
 
         val html = Format.removeSourceEditorFormatting(parser.toHtml(output), isInCalypsoMode, isInGutenbergMode)
 
-        val clipboard = context.getSystemService(Context.CLIPBOARD_SERVICE) as android.content.ClipboardManager
-        clipboard.primaryClip = ClipData.newHtmlText("aztec", output.toString(), html)
+        val clipboard = context.getSystemService(Context.CLIPBOARD_SERVICE) as ClipboardManager
+        clipboard.setPrimaryClip(ClipData.newHtmlText("aztec", output.toString(), html))
     }
 
     // copied from TextView with some changes

aztec/src/test/kotlin/org/wordpress/aztec/ClipboardTest.kt

@@ -346,7 +346,7 @@ class ClipboardTest {
 
         editText.setSelection(0)
         val clipboard = editText.context.getSystemService(Context.CLIPBOARD_SERVICE) as android.content.ClipboardManager
-        clipboard.primaryClip = ClipData.newPlainText("aztec", "Heading")
+        clipboard.setPrimaryClip(ClipData.newPlainText("aztec", "Heading"))
 
         TestUtils.pasteFromClipboard(editText)