Update perf-test Dockerfile to build TF 2.21 from source

TF 2.21's .bazelrc uses --enable_workspace, which requires Bazel 7+, so
bump the pinned bazel from 6.5.0 to 7.7.0 (matches TF 2.21's
.bazelversion). Also install xxd, which TF's XLA genrules now invoke
during the build.

Verified by running docker build of test/Dockerfile end-to-end: TF
wheel builds, save_application_examples.py converts all Keras
Application models, applications_performance loads and benchmarks them.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: Dobiasd

test/Dockerfile

@@ -6,13 +6,13 @@ FROM ubuntu:24.04
 RUN apt-get update -y --fix-missing
 ENV DEBIAN_FRONTEND=noninteractive
 RUN TZ=Etc/UTC apt-get -y install tzdata
-RUN apt-get install -y build-essential apt-utils cmake python3 python3-pip git llvm-17 clang-17 apt-transport-https curl gnupg patchelf
+RUN apt-get install -y build-essential apt-utils cmake python3 python3-pip git llvm-17 clang-17 apt-transport-https curl gnupg patchelf xxd
 
 RUN curl -fsSL https://bazel.build/bazel-release.pub.gpg | gpg --dearmor >bazel-archive-keyring.gpg
 RUN mv bazel-archive-keyring.gpg /usr/share/keyrings
 RUN echo "deb [arch=amd64 signed-by=/usr/share/keyrings/bazel-archive-keyring.gpg] https://storage.googleapis.com/bazel-apt stable jdk1.8" | tee /etc/apt/sources.list.d/bazel.list
-RUN apt-get update -y && apt-get install -y bazel-6.5.0
-RUN ln -s /usr/bin/bazel-6.5.0 /usr/bin/bazel
+RUN apt-get update -y && apt-get install -y bazel-7.7.0
+RUN ln -s /usr/bin/bazel-7.7.0 /usr/bin/bazel
 
 RUN git clone -b 'v2.21.0' --single-branch --depth 1 https://github.com/tensorflow/tensorflow.git
 WORKDIR /tensorflow