[SPARK-15827][BUILD] Publish Spark's forked sbt-pom-reader to Maven Central

Spark's SBT build currently uses a fork of the sbt-pom-reader plugin but depends on that fork via a SBT subproject which is cloned from https://github.com/scrapcodes/sbt-pom-reader/tree/ignore_artifact_id. This unnecessarily slows down the initial build on fresh machines and is also risky because it risks a build breakage in case that GitHub repository ever changes or is deleted.

In order to address these issues, I have published a pre-built binary of our forked sbt-pom-reader plugin to Maven Central under the `org.spark-project` namespace and have updated Spark's build to use that artifact. This published artifact was built from https://github.com/JoshRosen/sbt-pom-reader/tree/v1.0.0-spark, which contains the contents of ScrapCodes's branch plus an additional patch to configure the build for artifact publication.

/cc srowen ScrapCodes for review.

Author: Josh Rosen <[email protected]>

Closes #13564 from JoshRosen/use-published-fork-of-pom-reader.

(cherry picked from commit f74b777)
Signed-off-by: Josh Rosen <[email protected]>

Author: JoshRosen

project/plugins.sbt

@@ -21,3 +21,12 @@ libraryDependencies += "org.ow2.asm"  % "asm" % "5.0.3"
 libraryDependencies += "org.ow2.asm"  % "asm-commons" % "5.0.3"
 
 addSbtPlugin("com.simplytyped" % "sbt-antlr4" % "0.7.11")
+
+// Spark uses a custom fork of the sbt-pom-reader plugin which contains a patch to fix issues
+// related to test-jar dependencies (https://github.com/sbt/sbt-pom-reader/pull/14). The source for
+// this fork is published at https://github.com/JoshRosen/sbt-pom-reader/tree/v1.0.0-spark
+// and corresponds to commit b160317fcb0b9d1009635a7c5aa05d0f3be61936 in that repository.
+// In the long run, we should try to merge our patch upstream and switch to an upstream version of
+// the plugin; this is tracked at SPARK-14401.
+
+addSbtPlugin("org.spark-project" % "sbt-pom-reader" % "1.0.0-spark")