Fix mill build warnings about deprecated usages.

[DamianReeves]

Feature Request

Description of Problem:

Since upgrading to mill 0.11.x some used types are deprecated, address these deprecations.

[#0] [warn]     Jvm.runLocal("mdoc.Main", cp, dirParams)
[#0] [warn]     ^
[#0] [warn] /home/runner/work/morphir-scala/morphir-scala/project/modules/docs.sc:48:9: value Jvm in package modules is deprecated (since Mill 0.11.0-M9): use mill.util.Jvm
[#0] [warn]         Jvm.runLocal("mdoc.Main", cp, dirParams ++ Seq("--watch"))
[#0] [warn]         ^
[#0] [warn] /home/runner/work/morphir-scala/morphir-scala/project/modules/docs.sc:56:26: type Sources in package define is deprecated (since Mill after 0.11.0-M8): Use mill.define.Target instead.
[#0] [warn]   def docusaurusSources: Sources
[#0] [warn]                          ^
[#0] [warn] /home/runner/work/morphir-scala/morphir-scala/project/modules/docs.sc:57:22: type Sources in package define is deprecated (since Mill after 0.11.0-M8): Use mill.define.Target instead.
[#0] [warn]   def compiledMdocs: Sources
[#0] [warn]                      ^
[#0] [warn] /home/runner/work/morphir-scala/morphir-scala/project/modules/docs.sc:77:[19](https://github.com/finos/morphir-scala/actions/runs/5615735487/job/15216636429?pr=265#step:5:20): value Jvm in package modules is deprecated (since Mill 0.11.0-M9): use mill.util.Jvm
[#0] [warn]     val process = Jvm.spawnSubprocess(
[#0] [warn]                   ^
[#0] [warn] /home/runner/work/morphir-scala/morphir-scala/project/modules/docs.sc:153:14: value Jvm in package modules is deprecated (since Mill 0.11.0-M9): use mill.util.Jvm
[#0] [warn]     val p2 = Jvm.spawnSubprocess(
[#0] [warn]              ^
[#0] [warn] /home/runner/work/morphir-scala/morphir-scala/project/modules/docs.sc:169:5: value Jvm in package modules is deprecated (since Mill 0.11.0-M9): use mill.util.Jvm
[#0] [warn]     Jvm.runSubprocess(

[haesu]

Hi Damian. I made PR for this. Could you review it?
#287