RFR: 8344708: Compiler Implementation of Module Import Declarations [v2]

[Jan Lahoda]

> This is a patch to finalize the module imports feature. Please see:
> https://bugs.openjdk.org/browse/JDK-8344700

Jan Lahoda has updated the pull request incrementally with four additional commits since the last revision:

 - Cleanup, fixing tests.
 - Adjusting JShell defaults.
 - Fixing tests.
 - Cleanup - updated specification will permit requires transitive java.base; for all classfile versions; java.se no longer participates in preview.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/23801/files
  - new: https://git.openjdk.org/jdk/pull/23801/files/46c8454a..cffcf851

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=23801&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=23801&range=00-01

  Stats: 306 lines in 18 files changed: 219 ins; 50 del; 37 mod
  Patch: https://git.openjdk.org/jdk/pull/23801.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23801/head:pull/23801

PR: https://git.openjdk.org/jdk/pull/23801