Changed DefaultTextStyle to consider the TextTheme defined in the context for Bottom Nav Bar (#7042)

* Changed DefaultTextStyle to consider the TextTheme defined in the context

* added regression test for bottom nav bar text themes

* added second regression test for fixed navbar
diff --git a/AUTHORS b/AUTHORS
index e050455..e3f115f 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -10,3 +10,4 @@
 Michael Perrotte <mikemimik@gmail.com>
 Günter Zöchbauer <guenter@gzoechbauer.com>
 Raju Bitter <rajubitter@gmail.com>
+Michael Beckler <mcbeckler@gmail.com>