Fix incremental compilation when a Scala project depends on a Java project (#414)

* Upgrade ammonite to 1.1.2-30-53edc31

This is mainly to get https://github.com/lihaoyi/Ammonite/pull/851 which
should reduce the amount of unnecessary work done by incremental
compilation in the Mill build. This requires some code changes since
this means we now depend on a more recent version of coursier, as a
side-effect this means that we do not depend on scalaz anymore.

Also use the same ammonite version in the Mill build and in
ScalaModule#ammoniteReplClasspath.

Also remove an incorrect dependency in the caffeine integration test.
This was always wrong but did not start failing until this commit,
probably due to dependencies appearing in a different order on the
classpath.

* Rename ScalaWorker to ZincWorker

Starting with the next commit, it will be used in Java-only projects
too, so the name is misleading.

* Upgrade to Zinc 1.2.1

* Fix incremental compilation when a Scala project depends on a Java project

Before this commit, JavaModule#compile simply called javac
unconditionally, thus generating new classfiles every time. But if a
Scala project depends on a Java project, this will throw off the
incremental compilation algorithm which will unnecessarily recompile
files. To avoid this we now use Zinc to compile Java projects too (as a
bonus this means that Java compilation becomes incremental). This
required some refactoring in ZincWorkerImpl to be able to compile stuff
without having to pass Scala-specific options.

The issue solved by this commit could be reproduced by running in the
Mill repository:

$ mill main.compile
$ mill -i
@ main.compile()

and observing that before this commit, the `main.compile()` call ended
up recompiling code.

1 files changed, 3 insertions, 2 deletions

diff --git a/build.sc b/build.sc
index 456260d6..b2745404 100755
--- a/build.sc
+++ b/build.sc
@@ -85,7 +85,8 @@ object main extends MillModule {
     )
 
     def ivyDeps = Agg(
-      ivy"com.lihaoyi:::ammonite:1.1.2-6-27842d9",
+      // Keep synchronized with ammonite in Versions.scala
+      ivy"com.lihaoyi:::ammonite:1.1.2-30-53edc31",
       // Necessary so we can share the JNA classes throughout the build process
       ivy"net.java.dev.jna:jna:4.5.0",
       ivy"net.java.dev.jna:jna-platform:4.5.0"
@@ -176,7 +177,7 @@ object scalalib extends MillModule {
 
     def ivyDeps = Agg(
       // Keep synchronized with zinc in Versions.scala
-      ivy"org.scala-sbt::zinc:1.1.7"
+      ivy"org.scala-sbt::zinc:1.2.1"
     )
     def testArgs = Seq(
       "-DMILL_SCALA_WORKER=" + runClasspath().map(_.path).mkString(",")