RFR: 8313321 : Set minimum python version in WebKit cmake scripts

[Hima Bindu Meda]

Minimum version of python ,to run webkit build , on linux is set to 3.6 and for other platforms, minimum version of python is set to 3.8.

Verified build on all platforms. No issue seen

-------------

Commit messages:
 - Add check for python version for various platforms

Changes: https://git.openjdk.org/jfx/pull/1205/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1205&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8313321
  Stats: 18 lines in 1 file changed: 14 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jfx/pull/1205.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1205/head:pull/1205

PR: https://git.openjdk.org/jfx/pull/1205