Add bootclasspath_fragment as an alias for boot_image

This is part of the work to rename boot_image to bootclasspath_fragment
which is being done for two reasons:
1. To avoid clashing with the bootimg module type.
2. To better reflect what this represents.

While a bootclasspath_fragment can create what ART calls a boot image
(which is different to what the bootimg module type represents) it does
not have to do so.

Bug: 177892522
Test: m nothing
Change-Id: Ib45604be7adc790ded9e27a2ac812dd7522ca8db
diff --git a/apex/apex.go b/apex/apex.go
index 66c598c..80d9615 100644
--- a/apex/apex.go
+++ b/apex/apex.go
@@ -93,8 +93,14 @@
 	Multilib apexMultilibProperties
 
 	// List of boot images that are embedded inside this APEX bundle.
+	//
+	// deprecated: Use Bootclasspath_fragments
+	// TODO(b/177892522): Remove after has been replaced by Bootclasspath_fragments
 	Boot_images []string
 
+	// List of bootclasspath fragments that are embedded inside this APEX bundle.
+	Bootclasspath_fragments []string
+
 	// List of java libraries that are embedded inside this APEX bundle.
 	Java_libs []string
 
@@ -748,6 +754,7 @@
 	// Common-arch dependencies come next
 	commonVariation := ctx.Config().AndroidCommonTarget.Variations()
 	ctx.AddFarVariationDependencies(commonVariation, bootImageTag, a.properties.Boot_images...)
+	ctx.AddFarVariationDependencies(commonVariation, bootImageTag, a.properties.Bootclasspath_fragments...)
 	ctx.AddFarVariationDependencies(commonVariation, javaLibTag, a.properties.Java_libs...)
 	ctx.AddFarVariationDependencies(commonVariation, bpfTag, a.properties.Bpfs...)
 	ctx.AddFarVariationDependencies(commonVariation, fsTag, a.properties.Filesystems...)