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/subprojects/multi-module/groovy/build.gradle

@@ -0,0 +1,13 @@
+plugins {
+    id 'java'
+}
+
+allprojects {
+    repositories {
+        jcenter()
+    }
+}
+
+dependencies {
+    testImplementation 'junit:junit:4.12'
+}

fixtures/subprojects/multi-module/groovy/child-a/build.gradle

@@ -0,0 +1,7 @@
+plugins {
+    id 'java'
+}
+
+dependencies {
+    implementation 'com.squareup.okio:okio:2.2.2'
+}

fixtures/subprojects/multi-module/groovy/child-b/build.gradle

@@ -0,0 +1,8 @@
+plugins {
+    id 'java'
+}
+
+dependencies {
+    implementation project(':child-a')
+    implementation 'com.squareup.moshi:moshi:1.8.0'
+}

fixtures/subprojects/multi-module/groovy/settings.gradle

@@ -0,0 +1 @@
+include ':child-a', ':child-b'