Use sub-directory for 'setup-gradle' dist

To prepare for converting the 'dependency-submission' action into Typescript,
we move the 'setup-gradle' entry points and outputs into a sub-directory.

sources/src/setup-gradle/main.ts

@@ -0,0 +1,37 @@
+import * as core from '@actions/core'
+
+import * as setupGradle from '../setup-gradle'
+import * as execution from '../execution'
+import * as provisioner from '../provision'
+import * as layout from '../repository-layout'
+import * as params from '../input-params'
+
+/**
+ * The main entry point for the action, called by Github Actions for the step.
+ */
+export async function run(): Promise<void> {
+    try {
+        // Configure Gradle environment (Gradle User Home)
+        await setupGradle.setup()
+
+        // Download and install Gradle if required
+        const executable = await provisioner.provisionGradle()
+
+        // Only execute if arguments have been provided
+        const args: string[] = params.getArguments()
+        if (args.length > 0) {
+            const buildRootDirectory = layout.buildRootDirectory()
+            await execution.executeGradleBuild(executable, buildRootDirectory, args)
+        }
+    } catch (error) {
+        core.setFailed(String(error))
+        if (error instanceof Error && error.stack) {
+            core.info(error.stack)
+        }
+    }
+
+    // Explicit process.exit() to prevent waiting for hanging promises.
+    process.exit()
+}
+
+run()