RFR: 7903156: remove jopt-simple dependency from jextract [v5]

[Athijegannathan Sundararajan]

> removed jopt-simple dependency as well as moditect grade plugin dependency. Piggybacking build.gradle change to enforce 'jtreg_home' check in jtreg task's doFirst block.

Athijegannathan Sundararajan has updated the pull request incrementally with one additional commit since the last revision:

  accidentally moved CommandLine.java to a different dir. Fixed -C "-D Foo" handling.
  cleaned code and commented.

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Changes:
  - all: https://git.openjdk.java.net/jextract/pull/19/files
  - new: https://git.openjdk.java.net/jextract/pull/19/files/d68a258c..e021879a

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jextract&pr=19&range=04
 - incr: https://webrevs.openjdk.java.net/?repo=jextract&pr=19&range=03-04

  Stats: 41 lines in 4 files changed: 28 ins; 0 del; 13 mod
  Patch: https://git.openjdk.java.net/jextract/pull/19.diff
  Fetch: git fetch https://git.openjdk.java.net/jextract pull/19/head:pull/19

PR: https://git.openjdk.java.net/jextract/pull/19