RFR: 6925: Cache the local maven repo between runs [v3]

[Gunnar Morling]

> So this adds the caching of Maven dependencies we discussed in the other PR. While testing this in my fork, it reduced
> the build time from ~30 min to ~23 min. I'll reword the commit message if there's agreement on this and a Jira issue
> exists. Thanks!

Gunnar Morling has refreshed the contents of this pull request, and previous commits have been removed. The incremental
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  6925: Caching Maven repo

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Changes:
  - all: https://git.openjdk.java.net/jmc/pull/124/files
  - new: https://git.openjdk.java.net/jmc/pull/124/files/b17143b1..fd2b718f

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jmc&pr=124&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jmc&pr=124&range=01-02

  Stats: 0 lines in 0 files changed: 0 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jmc/pull/124.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/124/head:pull/124

PR: https://git.openjdk.java.net/jmc/pull/124