[foreign-abi] RFR: 8241148: need a way to create MemorySegment with contents from java String and a way to read a C char* as java String

[Athijegannathan Sundararajan]

Adding utility methods to ForeignUnsafe class.

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Commit messages:
 - 8241148: need a way to create MemorySegment with contents from java String and a way to read a C char* as java String

Changes: https://git.openjdk.java.net/panama-foreign/pull/55/files
 Webrev: https://webrevs.openjdk.java.net/panama-foreign/55/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8241148
  Stats: 154 lines in 3 files changed: 133 ins; 19 del; 2 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/55.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/55/head:pull/55

PR: https://git.openjdk.java.net/panama-foreign/pull/55