Treat each plugin as an individual source set

Adds separate build tasks for each plugin by auto-discovering plugin meta
files in the build script.  Each plugin will automatically have its
main sources and tests compiled, and then it's output added to the game
modules classpath.

This enables support for incremental compilation of scripts, as well as
unit testing using Gradle's test framework.

game/build.gradle

@@ -7,59 +7,23 @@ buildscript {
 
     dependencies {
         classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlinVersion"
+        classpath group: 'com.moandjiezana.toml', name: 'toml4j', version: '0.7.1'
     }
 }
 
-apply plugin: 'kotlin'
-
 ext.pluginsDir = "$projectDir/src/plugins"
 
-sourceSets {
-    plugins {
-        kotlin {
-            srcDir "$pluginsDir"
-            exclude 'stub.kt'
-            exclude '**/*.kts'
-        }
-    }
-}
+apply plugin: 'kotlin'
+apply from: 'plugins.gradle'
 
 dependencies {
     compile project(':cache')
     compile project(':net')
     compile project(':util')
 
-    pluginsCompile(configurations.compile)
-    pluginsCompile(sourceSets.main.output)
-
+    compile group: 'io.github.lukehutch', name: 'fast-classpath-scanner', version: '2.0.21'
     compile group: 'org.jetbrains.kotlin', name: 'kotlin-stdlib-jre8', version: "$kotlinVersion"
     compile group: 'org.jetbrains.kotlin', name: 'kotlin-compiler', version: "$kotlinVersion"
 
-    runtime files("$buildDir/plugins")
-    runtime sourceSets.plugins.output
-}
-
-
-task compilePluginScripts(type: JavaExec, dependsOn: [classes, pluginsClasses]) {
-    group = LifecycleBasePlugin.BUILD_GROUP
-    description = 'Compile plugin script files (.plugin.kts) to java bytecode'
-
-    def compilerClasspath = [
-            configurations.compile.asPath,
-            configurations.runtime.asPath,
-            sourceSets.main.compileClasspath.asPath,
-            sourceSets.main.runtimeClasspath.asPath
-    ]
-
-    def outputDir = "$buildDir/plugins"
-    def manifestPath = "$buildDir/plugins/manifest.txt"
-
-    inputs.source "$pluginsDir"
-    outputs.dir outputDir
-
-    classpath = sourceSets.main.compileClasspath + sourceSets.main.runtimeClasspath
-    main = 'org.apollo.game.plugin.kotlin.KotlinPluginCompiler'
-    args = ["$pluginsDir", outputDir, manifestPath, compilerClasspath.join(':')]
-}
-
-assemble.dependsOn compilePluginScripts
+    testCompile "org.jetbrains.kotlin:kotlin-test-junit:$kotlinVersion"
+}