RFR: JDK-8308028 Replace more uses of System.getProperty("os.name") with PlatformUtil calls [v3]

[Carl Döbbelin]

> replaced implementation of OS checks in HostUtils with calls of PlatformUtil

Carl Döbbelin has updated the pull request incrementally with one additional commit since the last revision:

  refactored HostUtils

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Changes:
  - all: https://git.openjdk.org/jfx/pull/1134/files
  - new: https://git.openjdk.org/jfx/pull/1134/files/28131e2d..a14bab71

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1134&range=02
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1134&range=01-02

  Stats: 11 lines in 1 file changed: 0 ins; 6 del; 5 mod
  Patch: https://git.openjdk.org/jfx/pull/1134.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1134/head:pull/1134

PR: https://git.openjdk.org/jfx/pull/1134