Update java_api_library prop name

Context
- Update java_api_library module's prop name from api_providers to
  api_contributions to adjust to module rename
- Update variables name correspondingly to enhance readability

Test: m
Change-Id: I93b941a572e04bed6084109d151ba83a82715651
diff --git a/java/java_test.go b/java/java_test.go
index 3f8cd8e..62c2845 100644
--- a/java/java_test.go
+++ b/java/java_test.go
@@ -1823,13 +1823,13 @@
 		java_api_library {
 			name: "bar1",
 			api_surface: "public",
-			api_providers: ["foo1"],
+			api_contributions: ["foo1"],
 		}
 
 		java_api_library {
 			name: "bar2",
 			api_surface: "system",
-			api_providers: ["foo1", "foo2"],
+			api_contributions: ["foo1", "foo2"],
 		}
 		`,
 		map[string][]byte{
@@ -1876,13 +1876,13 @@
 		java_api_library {
 			name: "bar1",
 			api_surface: "public",
-			api_providers: ["foo1"],
+			api_contributions: ["foo1"],
 		}
 
 		java_api_library {
 			name: "bar2",
 			api_surface: "system",
-			api_providers: ["foo1", "foo2"],
+			api_contributions: ["foo1", "foo2"],
 		}
 		`,
 		map[string][]byte{