RFR: 8357625: Build should generate platform specific shaders

[Ambarish Rapte]

On a given platform, the build generates prism and decora shader files for all platforms. 
Ideally it should generate only the platform specific shader files.

Fix:
Generate only platform specific hardware shaders.
sw pipeline shaders must be generated for all platforms.

But the hardware shaders, should be as:
1. Mac platform : metal and es2 shaders
2. Win platform: d3d shaders and if IS_INCLUDE_ES2 is true then es2 shaders as well
3. Linux : only es2 shaders

Verification:
Verified that the shaders are generated as expected. 
headul tests pass, apps launch correctly.

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Commit messages:
 - optimize creating shaders

Changes: https://git.openjdk.org/jfx/pull/2071/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=2071&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8357625
  Stats: 31 lines in 3 files changed: 22 ins; 1 del; 8 mod
  Patch: https://git.openjdk.org/jfx/pull/2071.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/2071/head:pull/2071

PR: https://git.openjdk.org/jfx/pull/2071