RFR: 8332497: javac prints an AssertionError when annotation processing runs on program with module imports [v16]

[Evemose]

> Fix is pretty simple: visitModuleImport in com.sun.tools.javac.tree.TreeScanner has notbeen overriden, so defaulted to Visitor::visitModuleImport, which forwards to Visitor::visitTree, which is also not overriden, and, therefore, threw AssertionError. 
> 
> PS: Im not even sure how it worked before without crashing, seems like there is some intermidiate implementation between this TreeScanner and actual scanners because otherwise it should have resultedin compile error the moment it encounter module importin any visitor

Evemose has updated the pull request incrementally with two additional commits since the last revision:

 - Merge remote-tracking branch 'origin/fix_module_imoprts_apt_fail' into fix_module_imoprts_apt_fail
   
   # Conflicts:
   #	test/langtools/tools/javac/processing/ModuleImportProcessingTest.java
 - moved test to processing folder

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Changes:
  - all: https://git.openjdk.org/jdk/pull/19292/files
  - new: https://git.openjdk.org/jdk/pull/19292/files/cf813cc4..3e4ec686

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19292&range=15
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19292&range=14-15

  Stats: 78 lines in 1 file changed: 63 ins; 1 del; 14 mod
  Patch: https://git.openjdk.org/jdk/pull/19292.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19292/head:pull/19292

PR: https://git.openjdk.org/jdk/pull/19292