RFR: JDK-8301990: Separate Arguments::parse into two phases [v2]

[Justin King]

> Separate out some logic from `Arguments::parse` into a separate preceding phase, preprocessing. See JDK-8301990 and JDK-8299196 for more details.

Justin King has updated the pull request incrementally with one additional commit since the last revision:

  Updates based on review
  
  Signed-off-by: Justin King <jcking at google.com>

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12458/files
  - new: https://git.openjdk.org/jdk/pull/12458/files/fd56b91b..20895b55

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12458&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12458&range=00-01

  Stats: 30 lines in 2 files changed: 4 ins; 6 del; 20 mod
  Patch: https://git.openjdk.org/jdk/pull/12458.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12458/head:pull/12458

PR: https://git.openjdk.org/jdk/pull/12458