Bug 1877157 - Set correct classpath on javadoc task. r=geckoview-reviewers,owlish,nalexander

It is unnecessary to join path with path separator when adding classpath
as file collection.

Also, javadoc's sourcepath argument have to use OS related path separator.
Default is OS related path separator, so we should use it instead.

Differential Revision: https://phabricator.services.mozilla.com/D201038

mobile/android/geckoview/build.gradle

@@ -322,14 +322,14 @@ android.libraryVariants.all { variant ->
         source = variant.sourceSets.collect({ it.java.srcDirs })
         exclude '**/R.java', '**/BuildConfig.java'
         include 'org/mozilla/geckoview/**.java'
-        options.addPathOption('sourcepath', ':').setValue(
+        options.addPathOption('sourcepath').setValue(
              variant.sourceSets.collect({ it.java.srcDirs }).flatten() +
              variant.generateBuildConfigProvider.get().sourceOutputDir.asFile.get() +
              variant.aidlCompileProvider.get().sourceOutputDir.asFile.get()
         )
         options.addStringOption("Xmaxwarns", "1000")
 
-        classpath += project.files(android.getBootClasspath().join(File.pathSeparator))
+        classpath += files(android.getBootClasspath())
         classpath += variant.javaCompileProvider.get().classpath
 
         options.memberLevel = JavadocMemberLevel.PROTECTED