Android OSS: Solve some Javadoc warning due to missing dependencies

Summary:
A bunch of deps were missing when generating Javadoc, producing warnings. One issue was:

```
project.getConfigurations().getByName("compile").asList()
```

Seems to be deprecated (?), so this list is always empty. The mitigation is to create a new configuration that just inherits from `api()` dependencies, so that we can add them in Javadoc task.

The other problem (not solved in this commit), is that some deps are .aar files, which require some manual unpacking before they can be processed: https://stackoverflow.com/questions/35853906/how-to-generate-javadoc-for-android-library-when-it-has-dependencies-which-are-a

Note that this is separate fix from facebook#30417

Changelog: [Internal]

Reviewed By: JoshuaGross

Differential Revision: D25041164

fbshipit-source-id: 2ee8b268c2d38e3ecbf622c05c3c56123b7a15a6

Author: fkgozali

ReactAndroid/build.gradle

@@ -436,6 +436,7 @@ android {
     configurations {
         extractHeaders
         extractJNI
+        javadocDeps.extendsFrom api
     }
 }
 
@@ -456,6 +457,8 @@ dependencies {
     extractHeaders("com.facebook.fbjni:fbjni:0.0.2:headers")
     extractJNI("com.facebook.fbjni:fbjni:0.0.2")
 
+    javadocDeps("com.squareup:javapoet:1.13.0")
+
     testImplementation("junit:junit:${JUNIT_VERSION}")
     testImplementation("org.powermock:powermock-api-mockito2:${POWERMOCK_VERSION}")
     testImplementation("org.powermock:powermock-module-junit4-rule:${POWERMOCK_VERSION}")

ReactAndroid/release.gradle

@@ -76,8 +76,9 @@ afterEvaluate { project ->
     task androidJavadoc(type: Javadoc, dependsOn: generateReleaseBuildConfig) {
         source = android.sourceSets.main.java.srcDirs
         classpath += files(android.bootClasspath)
-        classpath += files(project.getConfigurations().getByName("compile").asList())
         classpath += files("$buildDir/generated/source/buildConfig/release")
+        // Note: this doesn't handle .aar files, only .jar.
+        classpath += configurations.javadocDeps
         include("**/*.java")
     }