Change type of TARGET_BUILD_APPS from bool to list

TARGET_BUILD_APPS is supposed to be a list of apps to
build, so having it be a bool was incorrect. Change it
to properly reflect what it is, because the starlark
product configuration relies on soong's interpretation
of variables types.

Bug: 201700692
Test: Presubmits
Change-Id: I00109b57abbcda86077f0465f982f54b4a77a7f0
diff --git a/core/soong_config.mk b/core/soong_config.mk
index 4999464..fd60b71 100644
--- a/core/soong_config.mk
+++ b/core/soong_config.mk
@@ -37,7 +37,7 @@
 
 $(call add_json_bool, Allow_missing_dependencies,        $(filter true,$(ALLOW_MISSING_DEPENDENCIES)))
 $(call add_json_bool, Unbundled_build,                   $(TARGET_BUILD_UNBUNDLED))
-$(call add_json_bool, Unbundled_build_apps,              $(TARGET_BUILD_APPS))
+$(call add_json_list, Unbundled_build_apps,              $(TARGET_BUILD_APPS))
 $(call add_json_bool, Unbundled_build_image,             $(TARGET_BUILD_UNBUNDLED_IMAGE))
 $(call add_json_bool, Always_use_prebuilt_sdks,          $(TARGET_BUILD_USE_PREBUILT_SDKS))