Kotlin: clamp -language-version to 1.9

This is an experiment to see if compiling the 1.8 kotlin extractor with
`-language-version=1.9` will cause problems. It it works, it will allow
us to use a 2.3.x toolchain (which doesn't support 1.8 any more).

java/kotlin-extractor/versions.bzl

@@ -22,6 +22,8 @@ def version_less(lhs, rhs):
 
 def get_language_version(version):
     major, minor, _ = _version_to_tuple(version)
+    if major == 1 and minor < 9:
+        return "1.9"
     return "%s.%s" % (major, minor)
 
 def _basename(path):