[foreign-jextract] RFR: 8241925: jextract should generate simple allocation, access API for C primitive types

[Athijegannathan Sundararajan]

added static method helper classes to handle allocation, access ot C primitive types and C strings.

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Commit messages:
 - 8241925: jextract should generate simple allocation, access API for C primitive types

Changes: https://git.openjdk.java.net/panama-foreign/pull/78/files
 Webrev: https://webrevs.openjdk.java.net/panama-foreign/78/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8241925
  Stats: 627 lines in 11 files changed: 598 ins; 21 del; 8 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/78.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/78/head:pull/78

PR: https://git.openjdk.java.net/panama-foreign/pull/78