Allow access to the class jar for java_import using {.jar} tag

Layoutlib requires access to the jar file (containing .class) files for
a number of libraries including "core-libart". It does that using the
{.jar} output tag, e.g. "core-libart{.jar}".

This change makes sure that works when "core-libart" is provided as a
java_import instead of a java_library.

Bug: 142938164
Test: m nothing
Change-Id: I605019d680c28e4a33f0ca14279d63fa62b9774b

java/java_test.go

@@ -1412,7 +1412,31 @@ func TestJavaLibrary(t *testing.T) {
 						name: "core",
 						sdk_version: "none",
 						system_modules: "none",
-				}`),
+				}
+
+				filegroup {
+					name: "core-jar",
+					srcs: [":core{.jar}"],
+				}
+`),
+	})
+	ctx := testContext()
+	run(t, ctx, config)
+}
+
+func TestJavaImport(t *testing.T) {
+	config := testConfig(nil, "", map[string][]byte{
+		"libcore/Android.bp": []byte(`
+				java_import {
+						name: "core",
+						sdk_version: "none",
+				}
+
+				filegroup {
+					name: "core-jar",
+					srcs: [":core{.jar}"],
+				}
+`),
 	})
 	ctx := testContext()
 	run(t, ctx, config)