Respect CompilerConfiguration.sourceFiles in EclipseJavaCompiler

[famod]

Just like JavacCompiler does, to avoid "FilerException: Source file already created" during annotation processing when running mvn without clean after changing code.

Fixes #232

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The crucial thing here is that the compiler will run the annotation processors anyway, so it makes no sense to explicitly specify sources generated from the previous run.

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Without the change to EclipseJavaCompiler the new IT would fail with:

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.10.1:compile (default-compile) on project simple-javac: Compilation failure
[ERROR] /home/famod/proj/plexus-compiler/plexus-compiler-its/target/it/eclipse-compiler-mapstruct/src/main/java/CarMapper.java:[25,18] Internal error in the mapping processor: java.lang.RuntimeException: javax.annotation.processing.FilerException: Source file already exists : CarMapperImpl   at org.mapstruct.ap.internal.processor.MapperRenderingProcessor.createSourceFile(MapperRenderingProcessor.java:59)      at org.mapstruct.ap.internal.processor.MapperRenderingProcessor.writeToSourceFile(MapperRenderingProcessor.java:39)     at org.mapstruct.ap.internal.processor.MapperRenderingProcessor.process(MapperRenderingProcessor.java:29)       at org.mapstruct.ap.internal.processor.MapperRenderingProcessor.process(MapperRenderingProcessor.java:24)       at org.mapstruct.ap.MappingProcessor.process(MappingProcessor.java:350)        at org.mapstruct.ap.MappingProcessor.processMapperTypeElement(MappingProcessor.java:330)         at org.mapstruct.ap.MappingProcessor.processMapperElements(MappingProcessor.java:279)   at org.mapstruct.ap.MappingProcessor.process(MappingProcessor.java:174)         at org.eclipse.jdt.internal.compiler.apt.dispatch.RoundDispatcher.handleProcessor(RoundDispatcher.java:142)     at org.eclipse.jdt.internal.compiler.apt.dispatch.RoundDispatcher.round(RoundDispatcher.java:124)       at org.eclipse.jdt.internal.compiler.apt.dispatch.BaseAnnotationProcessorManager.processAnnotations(BaseAnnotationProcessorManager.java:172)    at org.eclipse.jdt.internal.compiler.Compiler.processAnnotations(Compiler.java:953)     at org.eclipse.jdt.internal.compiler.Compiler.compile(Compiler.java:450)        at org.eclipse.jdt.internal.compiler.Compiler.compile(Compiler.java:426)        at org.eclipse.jdt.internal.compiler.batch.Main.performCompilation(Main.java:4776)      at org.eclipse.jdt.internal.compiler.tool.EclipseCompilerImpl.call(EclipseCompilerImpl.java:100)        at org.eclipse.jdt.internal.compiler.tool.EclipseCompiler$1.call(EclipseCompiler.java:196)      at org.codehaus.plexus.compiler.eclipse.EclipseJavaCompiler.performCompile(EclipseJavaCompiler.java:374)        at org.apache.maven.plugin.compiler.AbstractCompilerMojo.execute(AbstractCompilerMojo.java:1209)        at org.apache.maven.plugin.compiler.CompilerMojo.execute(CompilerMojo.java:198)         at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:137)    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:210)      at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:156)      at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:148)      at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:117)     at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:81)      at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build(SingleThreadedBuilder.java:56)        at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:128)      at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:305)       at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:192)       at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:105)         at org.apache.maven.cli.MavenCli.execute(MavenCli.java:972)     at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:293)      at org.apache.maven.cli.MavenCli.main(MavenCli.java:196)        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)       at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)     at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)     at java.base/java.lang.reflect.Method.invoke(Method.java:568)   at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:282)          at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:225)          at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:406)        at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:347)  Caused by: javax.annotation.processing.FilerException: Source file already exists : CarMapperImpl         at org.eclipse.jdt.internal.compiler.apt.dispatch.BatchFilerImpl.createSourceFile(BatchFilerImpl.java:149)      at org.mapstruct.ap.internal.processor.MapperRenderingProcessor.createSourceFile(MapperRenderingProcessor.java:56)      ... 41 more

(sorry for the garbled output but that's the way it's printed out by compiler-plugin)

[famod]

So we are back to a list; I basically rolled back #230 because it doesn't make sense anymore.