RFR: 8254996: make jdk.net.UnixDomainPrincipal a record class

[Patrick Concannon]

Hi,

Could someone please review my code for JDK-8254996: 'make jdk.net.UnixDomainPrincipal a record class'?

`jdk.net.UnixDomainPrincipal` is a simple immutable data class that requires boilerplate methods for access. However, these methods and fields are susceptible to trivial mistakes and add to the verbosity of the class. 
This fix replaces the data class with a record class, a new type in JDK 16, making the code more concise and easier to maintain. This code is binary compatible with the original. For the generated API doc change, please refer to the specdiff attached to the CSR.

CSR : https://bugs.openjdk.java.net/browse/JDK-8257823

Kind regards,
Patrick

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Commit messages:
 - 8254996: make jdk.net.UnixDomainPrincipal a record class

Changes: https://git.openjdk.java.net/jdk/pull/1668/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1668&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8254996
  Stats: 52 lines in 1 file changed: 3 ins; 45 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1668.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1668/head:pull/1668

PR: https://git.openjdk.java.net/jdk/pull/1668