Rename UpdatableBootJars to ApexBootJars.

Note that ART apex boot jars and core-icu4j are exceptions here as they
are not part of ApexBootJars. ART apex boot jars are defined in their
own variable, while core-icu4j is treated as a regular non-updatable
boot jar.

Bug: 191127295
Test: atest CtsClasspathsTestCases
Change-Id: I3cea3d82ef521655a1a5ffa8cae2258ab9d08bfc
diff --git a/java/java.go b/java/java.go
index e38a714..b6e2a54 100644
--- a/java/java.go
+++ b/java/java.go
@@ -457,7 +457,7 @@
 
 var _ android.ApexModule = (*Library)(nil)
 
-// Provides access to the list of permitted packages from updatable boot jars.
+// Provides access to the list of permitted packages from apex boot jars.
 type PermittedPackagesForUpdatableBootJars interface {
 	PermittedPackagesForUpdatableBootJars() []string
 }