Avoid targeting Java 9 for targets with SDK version up to 29.

Targets with sdk_version values up to and including 29 should not use
Java language level 9, even if EXPERIMENTAL_JAVA_LANGUAGE_LEVEL_9=true
is set.

This change keeps the make logic in sync with the soong logic in the
other change in this topic.

Bug: 131678633
Test: EXPERIMENTAL_JAVA_LANGUAGE_LEVEL_9=true make droid tests docs cts java
Change-Id: Icd5db432f6b18486e8ede006c15a930c754ad4c2