Propagate min and max sdk versions to classpaths.proto configs.

These attributed define a range for dessert releases where the jars
should be active, and included in corresponding CLASSPATH varibles by
derive_classpath.

Bug: 190818041
Test: presubmit
Change-Id: Ieb9aef29657ad0694d48a63019f93faca2678252

android/config.go

@@ -765,6 +765,16 @@ func (c *config) PreviewApiLevels() []ApiLevel {
 	return levels
 }
 
+func (c *config) LatestPreviewApiLevel() ApiLevel {
+	level := NoneApiLevel
+	for _, l := range c.PreviewApiLevels() {
+		if l.GreaterThan(level) {
+			level = l
+		}
+	}
+	return level
+}
+
 func (c *config) AllSupportedApiLevels() []ApiLevel {
 	var levels []ApiLevel
 	levels = append(levels, c.FinalApiLevels()...)