Switch BootJars/UpdatableBootJars to ConfiguredJarList

This change:
* Switches BootJars/UpdatableBootJars fields of config.productVariables
  from []string to ConfiguredJarList.
* Updates BootJars() method to simply concatenate the jars list from
  the BootJars/UpdatableBootJars fields.
* Adds an UnmarshalJSON(..) method to ConfiguredJarList to support
  unmarshalling from a single string array to avoid having to change the
  format of the JSON file from which the configuration is loaded.
* Adds some additional calls to ConfiguredJarList(..) in tests to
  convert from []string to ConfiguredJarList. They pass nil as the
  ctx argument as there is no suitable PathContext which will cause any
  errors to be thrown using panic. That is reasonable for hard coded
  values in tests. A follow up change will clean up the calls to
  ConfiguredJarList(..).

Bug: 171479578
Test: m nothing
Change-Id: I59b94dafb479ccd8f0471ed802be175af57be271

android/config.go

@@ -1415,6 +1415,26 @@ func (l *ConfiguredJarList) BuildPaths(ctx PathContext, dir OutputPath) Writable
 	return paths
 }
 
+// Called when loading configuration from JSON into a configuration structure.
+func (l *ConfiguredJarList) UnmarshalJSON(b []byte) error {
+	// Try and unmarshal into a []string each item of which contains a pair
+	// <apex>:<jar>.
+	var list []string
+	err := json.Unmarshal(b, &list)
+	if err != nil {
+		// Did not work so return
+		return err
+	}
+
+	apexes, jars, err := splitListOfPairsIntoPairOfLists(list)
+	if err != nil {
+		return err
+	}
+	l.apexes = apexes
+	l.jars = jars
+	return nil
+}
+
 func ModuleStem(module string) string {
 	// b/139391334: the stem of framework-minus-apex is framework. This is hard coded here until we
 	// find a good way to query the stem of a module before any other mutators are run.
@@ -1494,9 +1514,8 @@ var earlyBootJarsKey = NewOnceKey("earlyBootJars")
 
 func (c *config) BootJars() []string {
 	return c.Once(earlyBootJarsKey, func() interface{} {
-		ctx := NullPathContext{Config{c}}
-		list := CreateConfiguredJarList(ctx,
-			append(CopyOf(c.productVariables.BootJars), c.productVariables.UpdatableBootJars...))
-		return list.CopyOfJars()
+		list := c.productVariables.BootJars.CopyOfJars()
+		list = append(list, c.productVariables.UpdatableBootJars.CopyOfJars()...)
+		return list
 	}).([]string)
 }