RFR: 8338290: Xcode project generator for hotspot [v3]

[Magnus Ihse Bursie]

> Add a make target to generate an Xcode project file for Hotspot. 
> 
> This PR is the result of a cooperation between me and @gerard-ziemski. Gerard developed the original Xcode generator (as a stand-alone project in https://github.com/gerard-ziemski/xcode), and I have written the build system "glue" to integrate it, and refactored the code to modern JDK standards.
> 
> Usage: Run `make hotspot-xcode-project`, and an Xcode project file will be generated in `build/$BUILD/xcode`. You can also have this automatically opened in Xcode by `make open-hotspot-xcode-project` (but note that for repeated runs of this, `make open-hotspot-xcode-project-only` is greatly preferred).

Magnus Ihse Bursie has updated the pull request incrementally with one additional commit since the last revision:

  Rename $1_LD_JSON to $1_LDFLAGS_FILE

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Changes:
  - all: https://git.openjdk.org/jdk/pull/20564/files
  - new: https://git.openjdk.org/jdk/pull/20564/files/64b3ae19..ffff6a16

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20564&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20564&range=01-02

  Stats: 3 lines in 2 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/20564.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20564/head:pull/20564

PR: https://git.openjdk.org/jdk/pull/20564