Add clang-format version 18 to requirements.in (#1039)

Higher versions of `clang-format` produce different outputs than the
version used to format what's currently in the repository. On a system
where the developer installs a system package for clang-format (using,
e.g., `apt install clang-format`), they may unknowingly get a different
version than what was used to format the code in the repository. If they
run `./scripts/format_all.sh` they may see many changes and not realize
that it's due to a different in clang-format versions.

Adding clang-format to `requirements.in` and regenerating
`requirements.txt` is an easy way to get a known version of
clang-format. Thankfully, requiring clang-format does not bring in other
dependencies, so this ends up being a fairly surgical intervention.

Author: mhucka

requirements.in

@@ -35,3 +35,4 @@ pylint==3.3.3
 nbformat==5.1.3
 nbclient==0.6.5
 tensorflow-docs
+clang-format~=18.1.0

requirements.txt

@@ -34,6 +34,8 @@ cirq-core==1.5.0
     #   cirq-google
 cirq-google==1.5.0
     # via -r requirements.in
+clang-format==18.1.8
+    # via -r requirements.in
 contourpy==1.3.2
     # via
     #   -r requirements.in