[foreign-jextract] RFR: 8252465: jextract generates wrong layout and varhandle when different structs have same named field

[Athijegannathan Sundararajan]

all tests pass. all samples jextract and run fine on Mac.

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Commit messages:
 - 8252465: jextract generates wrong layout and varhandle when different structs have same named field

Changes: https://git.openjdk.java.net/panama-foreign/pull/295/files
 Webrev: https://webrevs.openjdk.java.net/panama-foreign/295/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8252465
  Stats: 25 lines in 1 file changed: 21 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/295.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/295/head:pull/295

PR: https://git.openjdk.java.net/panama-foreign/pull/295