Text Painting Fuzzer (#12813)

Various improvements (in particular a new painting fuzzer) to the text manual test.

Some additional documentation.

A fix to Stack to remove an LTR bias: make unpositioned children apply "alignment".

Some more debugging information on RichText and Text.

A fix to the flutter tool to not crash when an RPC call throws an exception.

packages/flutter_tools/lib/src/vmservice.dart

diff --git a/packages/flutter_tools/lib/src/vmservice.dart b/packages/flutter_tools/lib/src/vmservice.dart
index 651c65a..7cfab01 100644
--- a/packages/flutter_tools/lib/src/vmservice.dart
+++ b/packages/flutter_tools/lib/src/vmservice.dart
@@ -738,6 +738,10 @@
     } on WebSocketChannelException catch (error) {
       throwToolExit('Error connecting to observatory: $error');
       return null;
+    } on rpc.RpcException catch (error) {
+      printError('Error ${error.code} received from application: ${error.message}');
+      printTrace('${error.data}');
+      return null;
     }
   }