RFR: 8258499: JavaFX: Move src.zip out of the lib directory

[Kevin Rushforth]

The JavaFX SDK bundle provides a set of modular jars in the `lib` directory. It provides a `src.zip` file for use by IDEs in that same `lib` directory. If a developer adds the `lib` directory to their application's module path in the IDE, it will try to load `src.zip` as if it were a jar file, and will fail. This is a pain point for developers using the SDK. 

The proposed solution is to move the `src.zip` file from the lib directory to the top directory of the SDK.

With this fix, the layout of the SDK will be:


<sdk>/
    bin/                      (Windows)
        <native libraries>    (Windows)

    legal/
        ...

    lib/
        *.jar
        <native libraries>    (macOS and Linux)

    src.zip


NOTES:
1. The JavaFX Eclipse plugin will need a minor change, which is tracked by eclipse-efx/efxclipse-eclipse#85.
2. This still needs to be tested on IntelliJ

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Commit messages:
 - 8258499: JavaFX: Move src.zip out of the lib directory

Changes: https://git.openjdk.java.net/jfx/pull/558/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=558&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8258499
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jfx/pull/558.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/558/head:pull/558

PR: https://git.openjdk.java.net/jfx/pull/558