[amber-docs] RFR: Update and restructure JEP list [v2]

[Nicolai Parlog]

> Update and restructure JEP list

Nicolai Parlog has updated the pull request incrementally with one additional commit since the last revision:

  Add preview JEPs as list

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Changes:
  - all: https://git.openjdk.org/amber-docs/pull/25/files
  - new: https://git.openjdk.org/amber-docs/pull/25/files/3d71700c..4c097611

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=amber-docs&pr=25&range=01
 - incr: https://webrevs.openjdk.org/?repo=amber-docs&pr=25&range=00-01

  Stats: 12 lines in 1 file changed: 0 ins; 0 del; 12 mod
  Patch: https://git.openjdk.org/amber-docs/pull/25.diff
  Fetch: git fetch https://git.openjdk.org/amber-docs.git pull/25/head:pull/25

PR: https://git.openjdk.org/amber-docs/pull/25