RFR: 7903644: typedef of anonymous struct generates a redundant class [v3]

[Maurizio Cimadamore]

> This PR tweaks jextract so that typedefs of anonymous structs only generate one class (that of the struct).
> 
> This required some changes in both `NameMangler` (to make sure that the special naming rule was applied), and then in `OutputFactory`, to make sure that in such case the typedef class is not emitted.
> 
> I've tweaked a number of tests which now reflect the "less verbose" jextract output - as such I don't think we need to add further tests.

Maurizio Cimadamore has updated the pull request incrementally with one additional commit since the last revision:

  Add comment

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Changes:
  - all: https://git.openjdk.org/jextract/pull/195/files
  - new: https://git.openjdk.org/jextract/pull/195/files/cff996eb..a85ddbed

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jextract&pr=195&range=02
 - incr: https://webrevs.openjdk.org/?repo=jextract&pr=195&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jextract/pull/195.diff
  Fetch: git fetch https://git.openjdk.org/jextract.git pull/195/head:pull/195

PR: https://git.openjdk.org/jextract/pull/195