RFR: 7903610: Missing handling for array fields with inline struct declaration

[Maurizio Cimadamore]

This patch adds a new method in `Utils` which helps visitors to obtain a scoped declaration given a type. This is used whenever the visitor logic needs to recurse on a declared type e.g. in a variable, or a typedef. The current logic only tests for `Type.Declared` and, in doing so, misses some cases, such as arrays and typedefs which point back to a declared type.

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Commit messages:
 - Fix tabs
 - Add test
 - Initial push

Changes: https://git.openjdk.org/jextract/pull/161/files
 Webrev: https://webrevs.openjdk.org/?repo=jextract&pr=161&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903610
  Stats: 143 lines in 7 files changed: 119 ins; 11 del; 13 mod
  Patch: https://git.openjdk.org/jextract/pull/161.diff
  Fetch: git fetch https://git.openjdk.org/jextract.git pull/161/head:pull/161

PR: https://git.openjdk.org/jextract/pull/161