Initial version for thomaswue with Oracle GraalVM Native Image

* Initial version.

* Make PGO feature optional off-by-default. Needs PGO_MODE environment
variable to be set. Add -O3 -march=native tuning flags for better
performance.

* Adjust script to be more quiet.

* Adjust max city length. Fix an issue when accumulating results.

* Tune thomaswue submission.
mmap the entire file, use Unsafe directly instead of ByteBuffer, avoid byte[] copies.
These tricks give a ~30% speedup, over an already fast implementation.

* Optimize parsing of numbers based on specific given constraints.

* Fix for segment calculation for case of very small input.

* Minor shell script fixes.

* Separate out build step into file additional_build_step_thomaswue.sh,
simplify run script and remove PGO option for now.

* Minor corrections to the run script.

---------

Co-authored-by: Alfonso² Peterssen <alfonso.peterssen@oracle.com>

calculate_average_thomaswue.sh

@@ -0,0 +1,29 @@
+#!/bin/sh
+#
+#  Copyright 2023 The original authors
+#
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+#
+
+
+if [ -f ./image_calculateaverage_thomaswue ]; then
+    echo "Picking up existing native image, delete the file to select JVM mode." 1>&2
+    time ./image_calculateaverage_thomaswue
+else
+    source "$HOME/.sdkman/bin/sdkman-init.sh"
+    sdk use java 21.0.1-graal 1>&2
+    JAVA_OPTS="--enable-preview"
+    echo "Chosing to run the app in JVM mode as no native image was found, use additional_build_step_thomaswue.sh to generate." 1>&2
+    time java $JAVA_OPTS --class-path target/average-1.0.0-SNAPSHOT.jar dev.morling.onebrc.CalculateAverage_thomaswue
+fi
+