RFR: 8306281: function isWsl() returns false on WSL2

[Ivan Bereziuk]

Currently _isWsl()_ function is looking for "Microsoft" string in the _kernel release_ string (`$ uname -r`). 
That's not always true. Namely, on Ubuntu 22.04 - currently the newest Ubuntu LTS and default OS for WSL in Microsoft Store. In there `$ uname -r` command outputs "5.10.102.1-microsoft-standard-WSL2".
This makes _isWsl()_ function to return `false` in such environments and breaks JDK builds on WSL.

To correct that I made the substring search case-insensitive.

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Commit messages:
 - 8306281: function isWsl() returns false on WSL2

Changes: https://git.openjdk.org/jdk/pull/14413/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14413&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8306281
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/14413.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14413/head:pull/14413

PR: https://git.openjdk.org/jdk/pull/14413