Repeat kapt processor argument for multiple processors

kapt claims to support a comma separated list of annotation
processors, but it errors if multiple annotation processors
are given.  Surrounding the the list with {} does not error,
but it also doesn't even warn if the second element in the
list is garbage, so it may not be running the second
processor.  Repeat the processor argument for each
annotation processor class instead.

Bug: 154736649
Test: TestKapt
Test: m checkbuild
Change-Id: I4c7c161dbf867d7fba1aaf16fd5e502647e3f682

java/java.go

@@ -1130,7 +1130,8 @@ func (j *Module) collectBuilderFlags(ctx android.ModuleContext, deps deps) javaB
 	flags.java9Classpath = append(flags.java9Classpath, deps.java9Classpath...)
 	flags.processorPath = append(flags.processorPath, deps.processorPath...)
 
-	flags.processor = strings.Join(deps.processorClasses, ",")
+	flags.processors = append(flags.processors, deps.processorClasses...)
+	flags.processors = android.FirstUniqueStrings(flags.processors)
 
 	if len(flags.bootClasspath) == 0 && ctx.Host() && !flags.javaVersion.usesJavaModules() &&
 		decodeSdkDep(ctx, sdkContext(j)).hasStandardLibs() {
@@ -1265,7 +1266,7 @@ func (j *Module) compile(ctx android.ModuleContext, aaptSrcJar android.Path) {
 			srcJars = append(srcJars, kaptSrcJar)
 			// Disable annotation processing in javac, it's already been handled by kapt
 			flags.processorPath = nil
-			flags.processor = ""
+			flags.processors = nil
 		}
 
 		kotlinJar := android.PathForModuleOut(ctx, "kotlin", jarName)