RFR: JDK-8307807 Replace use of System.getProperty("os.name") with PlatformUtil calls [v2]

[Carl Döbbelin]

> Replaced querying of `System.getProperty("os.name")` to check for OS with the use of the methods provided by `PlatformUtils`

Carl Döbbelin has updated the pull request incrementally with two additional commits since the last revision:

 - Merge branch 'JDK-8307807-replace-system-getproperty-osname-platform-utils' of https://github.com/EstelonAgarwaen/jfx into JDK-8307807-replace-system-getproperty-osname-platform-utils
 - fixed linebreak and used platform util in launcherimpl

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Changes:
  - all: https://git.openjdk.org/jfx/pull/1132/files
  - new: https://git.openjdk.org/jfx/pull/1132/files/2f954d65..43c07589

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1132&range=01
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1132&range=00-01

  Stats: 24 lines in 3 files changed: 21 ins; 1 del; 2 mod
  Patch: https://git.openjdk.org/jfx/pull/1132.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1132/head:pull/1132

PR: https://git.openjdk.org/jfx/pull/1132