Extend InputDecoration with prefix/suffix padding (#19514)

Add widget valued prefix and suffix properties to InputDecoration.  These new properties are alternatives to prefixText and suffixText.
diff --git a/AUTHORS b/AUTHORS
index c8e76db..c51aaf954 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -24,4 +24,5 @@
 Dan Field <dfield@gmail.com>
 Noah Groß <gross@ngsger.de>
 Victor Choueiri <victor@ctrlanddev.com>
+Christian Mürtz <teraarts@t-online.de>
 Lukasz Piliszczuk <lukasz@intheloup.io>