Prepare for release 2.54.0 (#9601)

diff --git a/flutter-candidate.txt b/flutter-candidate.txt
index 6077c7b..b8f91c9 100644
--- a/flutter-candidate.txt
+++ b/flutter-candidate.txt

@@ -1 +1 @@
-fede7e6a0371993322a5aa122de6889bd83a9207
+71348e7b2b1b64e425fa0a3733f27d2b94ca7847

diff --git a/packages/devtools_app/lib/devtools.dart b/packages/devtools_app/lib/devtools.dart
index 5a3c204..caba9b5 100644
--- a/packages/devtools_app/lib/devtools.dart
+++ b/packages/devtools_app/lib/devtools.dart

@@ -10,4 +10,4 @@
 /// Note: a regexp in the `dt update-version' command logic matches the constant
 /// declaration `const version =`. If you change the declaration you must also
 /// modify the regex in the `dt update-version' command logic.
-const version = '2.54.0-dev.0';
+const version = '2.54.0';

diff --git a/packages/devtools_app/lib/src/framework/scaffold/scaffold.dart b/packages/devtools_app/lib/src/framework/scaffold/scaffold.dart
index 978f7b3..8c34b71 100644
--- a/packages/devtools_app/lib/src/framework/scaffold/scaffold.dart
+++ b/packages/devtools_app/lib/src/framework/scaffold/scaffold.dart

@@ -360,7 +360,7 @@
                           splitters: const [
                             DefaultSplitter(
                               key: BottomPane.splitterKey,
-                              isHorizontal: true,
+                              isHorizontal: false,
                             ),
                           ],
                           children: [

diff --git a/packages/devtools_app/pubspec.yaml b/packages/devtools_app/pubspec.yaml
index 43f47b8..e17f6a0 100644
--- a/packages/devtools_app/pubspec.yaml
+++ b/packages/devtools_app/pubspec.yaml

@@ -7,7 +7,7 @@
 
 # Note: this version should only be updated by running the 'dt update-version'
 # command that updates the version here and in 'devtools.dart'.
-version: 2.54.0-dev.0
+version: 2.54.0
 
 repository: https://github.com/flutter/devtools/tree/master/packages/devtools_app