Compile plugins at build-time instead of runtime

Adds gradle tasks to build all plugin scripts under data/plugins with
the KotlinPluginCompiler implementation previously used for runtime code
generation.  In addition to .plugin.kts files, scripts can also declare
API code in .kt files which will also be included on the classpath and
made available to other plugins.

game/build.gradle

@@ -14,9 +14,15 @@ apply plugin: 'kotlin'
 
 sourceSets {
     main.kotlin.srcDirs += 'src/kotlin'
+    main.kotlin.excludes += 'stub.kt'
+    main.kotlin.excludes += '**/*.kts'
 
     plugins {
-        kotlin.srcDirs += 'data/plugins'
+        kotlin {
+            srcDir 'data/plugins'
+            exclude 'stub.kt'
+            exclude '**/*.kts'
+        }
     }
 }
 
@@ -28,6 +34,33 @@ dependencies {
     pluginsCompile(configurations.compile)
     pluginsCompile(sourceSets.main.output)
 
-    compile group: 'org.jetbrains.kotlin', name: 'kotlin-compiler', version: "$kotlinVersion"
     compile group: 'org.jetbrains.kotlin', name: 'kotlin-stdlib-jre8', version: "$kotlinVersion"
+    compile group: 'org.jetbrains.kotlin', name: 'kotlin-compiler', version: "$kotlinVersion"
+
+    runtime files("$buildDir/plugins")
+    runtime sourceSets.plugins.output
 }
+
+
+task('compilePluginScripts', dependsOn: [classes, pluginsClasses], type: JavaExec) {
+    def compilerClasspath = [
+            configurations.compile.asPath,
+            configurations.runtime.asPath,
+            sourceSets.main.compileClasspath.asPath,
+            sourceSets.main.runtimeClasspath.asPath
+    ]
+
+    def inputDir = "$projectDir/data/plugins"
+    def outputDir = "$buildDir/plugins"
+    def manifestPath = "$buildDir/plugins/manifest.txt"
+
+    inputs.source inputDir
+    outputs.dir outputDir
+
+    println compilerClasspath.join(':')
+    classpath = sourceSets.main.compileClasspath + sourceSets.main.runtimeClasspath
+    main = 'org.apollo.game.plugin.kotlin.KotlinPluginCompiler'
+    args = [inputDir, outputDir, manifestPath, compilerClasspath.join(':')]
+}
+
+assemble.dependsOn(compilePluginScripts)