Rename BootImageModule to BootclasspathFragmentModule

Also renames files, tests, module types in a similar fashion.

There are still some references to image and boot image. They are kept
for the following reasons:
* image_name - this is the name of an ART boot image, i.e. the
  collection of .art/.oat/.vdex files.
* BootImageInfo - again this is related to the ART boot image.
* .../art_boot_images/... paths - ditto.

Bug: 177892522
Test: m nothing
Change-Id: Ie1f4738061d131fee75de48bc26a7601481bad4d

java/Android.bp

@@ -29,9 +29,9 @@ bootstrap_go_package {
         "app_import.go",
         "app_set.go",
         "base.go",
-        "boot_image.go",
         "boot_jars.go",
         "bootclasspath.go",
+        "bootclasspath_fragment.go",
         "builder.go",
         "classpath_fragment.go",
         "device_host_converter.go",
@@ -73,7 +73,7 @@ bootstrap_go_package {
         "app_import_test.go",
         "app_set_test.go",
         "app_test.go",
-        "boot_image_test.go",
+        "bootclasspath_fragment_test.go",
         "device_host_converter_test.go",
         "dexpreopt_test.go",
         "dexpreopt_bootjars_test.go",