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/android/variable.go b/android/variable.go
index bbb9868..c4cd6d2 100644
--- a/android/variable.go
+++ b/android/variable.go
@@ -252,8 +252,8 @@
 	UncompressPrivAppDex             *bool    `json:",omitempty"`
 	ModulesLoadedByPrivilegedModules []string `json:",omitempty"`
 
-	BootJars          ConfiguredJarList `json:",omitempty"`
-	UpdatableBootJars ConfiguredJarList `json:",omitempty"`
+	BootJars     ConfiguredJarList `json:",omitempty"`
+	ApexBootJars ConfiguredJarList `json:",omitempty"`
 
 	IntegerOverflowExcludePaths []string `json:",omitempty"`
 
@@ -442,8 +442,8 @@
 		Malloc_pattern_fill_contents: boolPtr(false),
 		Safestack:                    boolPtr(false),
 
-		BootJars:          ConfiguredJarList{apexes: []string{}, jars: []string{}},
-		UpdatableBootJars: ConfiguredJarList{apexes: []string{}, jars: []string{}},
+		BootJars:     ConfiguredJarList{apexes: []string{}, jars: []string{}},
+		ApexBootJars: ConfiguredJarList{apexes: []string{}, jars: []string{}},
 	}
 
 	if runtime.GOOS == "linux" {