Extract AotGenerateMojo to its own structure

This commit stops AotGenerateMojo from being an extension of the
regular run infrastructure and used the opportunity to extract a
number of utility classes to run a Java process.

As a result, not all features of running an application is supported
and exposed options now are targeted against AOT.

See gh-31682

spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/test/java/org/springframework/boot/maven/CommandLineBuilderTests.java

@@ -0,0 +1,78 @@
+/*
+ * Copyright 2012-2022 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.boot.maven;
+
+import java.util.Map;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.boot.maven.sample.ClassWithMainMethod;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link CommandLineBuilder}.
+ *
+ * @author Stephane Nicoll
+ */
+class CommandLineBuilderTests {
+
+	public static final String CLASS_NAME = ClassWithMainMethod.class.getName();
+
+	@Test
+	void buildWithNullJvmArgumentsIsIgnored() {
+		assertThat(CommandLineBuilder.forMainClass(CLASS_NAME).withJvmArguments((String[]) null).build())
+				.containsExactly(CLASS_NAME);
+	}
+
+	@Test
+	void buildWithNullIntermediateJvmArgumentIsIgnored() {
+		assertThat(CommandLineBuilder.forMainClass(CLASS_NAME).withJvmArguments("-verbose:class", null, "-verbose:gc")
+				.build()).containsExactly("-verbose:class", "-verbose:gc", CLASS_NAME);
+	}
+
+	@Test
+	void buildWithJvmArgument() {
+		assertThat(CommandLineBuilder.forMainClass(CLASS_NAME).withJvmArguments("-verbose:class").build())
+				.containsExactly("-verbose:class", CLASS_NAME);
+	}
+
+	@Test
+	void buildWithNullSystemPropertyIsIgnored() {
+		assertThat(CommandLineBuilder.forMainClass(CLASS_NAME).withSystemProperties(null).build())
+				.containsExactly(CLASS_NAME);
+	}
+
+	@Test
+	void buildWithSystemProperty() {
+		assertThat(CommandLineBuilder.forMainClass(CLASS_NAME).withSystemProperties(Map.of("flag", "enabled")).build())
+				.containsExactly("-Dflag=\"enabled\"", CLASS_NAME);
+	}
+
+	@Test
+	void buildWithNullArgumentsIsIgnored() {
+		assertThat(CommandLineBuilder.forMainClass(CLASS_NAME).withArguments((String[]) null).build())
+				.containsExactly(CLASS_NAME);
+	}
+
+	@Test
+	void buildWithNullIntermediateArgumentIsIgnored() {
+		assertThat(CommandLineBuilder.forMainClass(CLASS_NAME).withArguments("--test", null, "--another").build())
+				.containsExactly(CLASS_NAME, "--test", "--another");
+	}
+
+}