Initial ffm support

- Starter for jline ffm terminal provider
- Build changes for compiling with gradle toolchains
  defaulting to jdk22
- spring-shell-sample-ffm which compiles with jdk22
- ci workflow setups jdk 17/22
- Relates #1131

buildSrc/build.gradle

@@ -52,5 +52,9 @@ gradlePlugin {
 			id = "org.springframework.shell.sample"
 			implementationClass = "org.springframework.shell.gradle.SamplePlugin"
 		}
+		toolchainPlugin {
+			id = "org.springframework.shell.toolchain"
+			implementationClass = "org.springframework.shell.gradle.ToolchainPlugin"
+		}
 	}
 }

buildSrc/src/main/java/org/springframework/shell/gradle/ToolchainExtension.java

@@ -0,0 +1,42 @@
+/*
+ * Copyright 2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.shell.gradle;
+
+import org.gradle.api.Project;
+import org.gradle.api.provider.Property;
+import org.gradle.jvm.toolchain.JavaLanguageVersion;
+
+public class ToolchainExtension {
+
+	private final Property<JavaLanguageVersion> maximumCompatibleJavaVersion;
+
+	private final JavaLanguageVersion javaVersion;
+
+	public ToolchainExtension(Project project) {
+		this.maximumCompatibleJavaVersion = project.getObjects().property(JavaLanguageVersion.class);
+		String toolchainVersion = (String) project.findProperty("toolchainVersion");
+		this.javaVersion = (toolchainVersion != null) ? JavaLanguageVersion.of(toolchainVersion) : null;
+	}
+
+	public Property<JavaLanguageVersion> getMaximumCompatibleJavaVersion() {
+		return this.maximumCompatibleJavaVersion;
+	}
+
+	JavaLanguageVersion getJavaVersion() {
+		return this.javaVersion;
+	}
+
+}

buildSrc/src/main/java/org/springframework/shell/gradle/ToolchainPlugin.java

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.shell.gradle;
+
+import org.gradle.api.Plugin;
+import org.gradle.api.Project;
+import org.gradle.api.plugins.JavaPluginExtension;
+import org.gradle.jvm.toolchain.JavaLanguageVersion;
+import org.gradle.jvm.toolchain.JavaToolchainSpec;
+
+public class ToolchainPlugin implements Plugin<Project> {
+
+	@Override
+	public void apply(Project project) {
+		configureToolchain(project);
+	}
+
+	private void configureToolchain(Project project) {
+		ToolchainExtension toolchain = project.getExtensions().create("toolchain", ToolchainExtension.class, project);
+		project.afterEvaluate((evaluated) -> configure(evaluated, toolchain));
+	}
+
+	private void configure(Project project, ToolchainExtension toolchain) {
+		JavaLanguageVersion toolchainVersion = toolchain.getJavaVersion();
+		if (toolchainVersion == null) {
+			toolchainVersion = JavaLanguageVersion.of(22);
+		}
+		JavaToolchainSpec toolchainSpec = project.getExtensions()
+			.getByType(JavaPluginExtension.class)
+			.getToolchain();
+		toolchainSpec.getLanguageVersion().set(toolchainVersion);
+	}
+
+}