apex_key bp2build: disambiguate module and src deps.

(and remove unused keyName field.)

The private_key and public_key props of an apex_key can point to either
a module or a string. If it's a module, then respect it. If it's a
string, there's additional product variable lookup to find the apex_key
files in product_vars's DefaultAppCertificate parent dir.

This is similar to android_app_certificate.

Test: presubmits
Change-Id: Ib258da14cb0c2df8b5f817fcbc46afebcf225db8
diff --git a/bp2build/apex_key_conversion_test.go b/bp2build/apex_key_conversion_test.go
index 15bccf7..79b1d89 100644
--- a/bp2build/apex_key_conversion_test.go
+++ b/bp2build/apex_key_conversion_test.go
@@ -27,11 +27,12 @@
 }
 
 func registerApexKeyModuleTypes(ctx android.RegistrationContext) {
+	ctx.RegisterModuleType("filegroup", android.FileGroupFactory)
 }
 
-func TestApexKeySimple(t *testing.T) {
+func TestApexKeySimple_KeysAreSrcFiles(t *testing.T) {
 	runApexKeyTestCase(t, Bp2buildTestCase{
-		Description:                "apex key - simple example",
+		Description:                "apex key - keys are src files, use key_name attributes",
 		ModuleTypeUnderTest:        "apex_key",
 		ModuleTypeUnderTestFactory: apex.ApexKeyFactory,
 		Filesystem:                 map[string]string{},
@@ -43,8 +44,29 @@
 }
 `,
 		ExpectedBazelTargets: []string{MakeBazelTargetNoRestrictions("apex_key", "com.android.apogee.key", AttrNameToString{
-			"private_key": `"com.android.apogee.pem"`,
-			"public_key":  `"com.android.apogee.avbpubkey"`,
+			"private_key_name": `"com.android.apogee.pem"`,
+			"public_key_name":  `"com.android.apogee.avbpubkey"`,
+		}),
+		}})
+}
+
+func TestApexKey_KeysAreModules(t *testing.T) {
+	runApexKeyTestCase(t, Bp2buildTestCase{
+		Description:                "apex key - keys are modules, use key attributes",
+		ModuleTypeUnderTest:        "apex_key",
+		ModuleTypeUnderTestFactory: apex.ApexKeyFactory,
+		Filesystem:                 map[string]string{},
+		Blueprint: `
+apex_key {
+        name: "com.android.apogee.key",
+        public_key: ":com.android.apogee.avbpubkey",
+        private_key: ":com.android.apogee.pem",
+}
+` + simpleModuleDoNotConvertBp2build("filegroup", "com.android.apogee.avbpubkey") +
+			simpleModuleDoNotConvertBp2build("filegroup", "com.android.apogee.pem"),
+		ExpectedBazelTargets: []string{MakeBazelTargetNoRestrictions("apex_key", "com.android.apogee.key", AttrNameToString{
+			"private_key": `":com.android.apogee.pem"`,
+			"public_key":  `":com.android.apogee.avbpubkey"`,
 		}),
 		}})
 }