RFR: 8266318: Switch to macos prefix for macOS bundles

[Mikael Vidstedt]

Apple rebranded the operating system as "macOS" back in 2016. The JDK bundles files are still use the legacy "osx" string. They should be modernized to use "macos" instead.

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Commit messages:
 - 8266318: Switch to macos prefix for macOS bundles

Changes: https://git.openjdk.java.net/jdk/pull/3801/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3801&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8266318
  Stats: 11 lines in 2 files changed: 2 ins; 4 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3801.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3801/head:pull/3801

PR: https://git.openjdk.java.net/jdk/pull/3801