RFR: 7903697: Support symbols in header files are alias for different name in share library

[Maurizio Cimadamore]

This PR restores a functionality that was available in a (much) older version of jextract.

Basically, some library symbols can have a C name that differs from the symbol found in the shared library. This is typically done using an attribute (AsmLabelAttr). We already have code to parse declaration attributes, but when we switched to the new FFM-based jextract, we didn't update code generation to use the aliased name for the symbol lookup, if one was available.

I've resurrected the old test to check this functionality, with some changes: the original test also tested Windows support, but that seems less important, given that Windows doesn't really have an equivalent feature/attribute.

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Commit messages:
 - Initial push

Changes: https://git.openjdk.org/jextract/pull/232/files
  Webrev: https://webrevs.openjdk.org/?repo=jextract&pr=232&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903697
  Stats: 208 lines in 5 files changed: 203 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jextract/pull/232.diff
  Fetch: git fetch https://git.openjdk.org/jextract.git pull/232/head:pull/232

PR: https://git.openjdk.org/jextract/pull/232