Silence setlocale warnings in Java stub

Since 17cfa01, the java_stub_template.txt file calls into the locale tool to check for the presence of cetain locales.  These calls correctly send error messages to stderr.

Unfortunately, *bash* itself is doing locale lookups as soon as it sees that the LANG or LC_* variables are touched, and this results in warnings that pollute the output.  In our builds, the output is polluted with hundreds of warnings like these:

```
bazel-out/aarch64-opt-exec-CF41B97/bin/external/bfg/lang/java/src/main/java/com/google/devtools/build/bfg/JavaSourceFileParserCli: line 100: warning: setlocale: LC_CTYPE: cannot change locale (): No such file or directory
bazel-out/aarch64-opt-exec-CF41B97/bin/external/bfg/lang/java/src/main/java/com/google/devtools/build/bfg/JavaSourceFileParserCli: line 102: warning: setlocale: LC_CTYPE: cannot change locale (): No such file or directory
```

There is nothing we can do to avoid these warnings.  Trying to set the LANG or LC_* variables via --action_env and --host_action_env has no effect (other than trigger more/different warnings).

The problem stems from https://bugzilla.redhat.com/show_bug.cgi?id=1361965, which has been fixed in various distros but hasn't made its way to the one we are currently using.

Given that it's bash that is complaining, we can easily side-step this issue by patching the template and wrapping the problematic invocations behind "env".  In this way, bash never gets to see the locale changes. This change does precisely this.

Closes bazelbuild#17670.

PiperOrigin-RevId: 515350095
Change-Id: I1887003802aa329e7fb96f644a2fba906daf5165

src/main/java/com/google/devtools/build/lib/bazel/rules/java/java_stub_template.txt

@@ -97,9 +97,15 @@ function is_macos() {
 function available_utf8_locale() {
   # Both C.UTF-8 and en_US.UTF-8 do not cause any language-specific effects
   # when set as LC_CTYPE, but neither is certain to exist on all systems.
-  if [[ $(LC_CTYPE=C.UTF-8 locale charmap 2>/dev/null) == "UTF-8" ]]; then
+  #
+  # https://github.com/bazelbuild/bazel/pull/17670: Note that the use of "env"
+  # is important in these calls. Without "env", bash itself seems to pick up
+  # the LC_CTYPE change as soon as the variable is defined and may emit a
+  # warning when the locale files are not present. By using "env", bash never
+  # sees the change and the 2>/dev/null redirection does the right thing.
+  if [[ "$(env LC_CTYPE=C.UTF-8 locale charmap 2>/dev/null)" == "UTF-8" ]]; then
     echo "C.UTF-8"
-  elif [[ $(LC_CTYPE=en_US.UTF-8 locale charmap 2>/dev/null) == "UTF-8" ]]; then
+  elif [[ "$(env LC_CTYPE=en_US.UTF-8 locale charmap 2>/dev/null)" == "UTF-8" ]]; then
     echo "en_US.UTF-8"
   fi
 }