Use custom dependency resolution

- Use Apache Ivy to resolve artifact URLs
- Update build model with full artifact IDs
- Generate Maven module metadata to support dynamic version constraints
- Resolve snapshot versions and generate snapshot metadata
- Add test fixtures and rewrite Gradle plugin tests
- Update dependencies

fixtures/basic/basic-java-project/groovy/build.gradle

@@ -0,0 +1,13 @@
+plugins {
+    id 'java'
+}
+
+repositories {
+    jcenter()
+    mavenCentral()
+}
+
+dependencies {
+    implementation 'com.squareup.okio:okio:2.2.2'
+    implementation 'com.squareup.moshi:moshi:1.8.0'
+}