Runtime envdef handles case-insensitive environment variable names on Windows.

[mitchell-as]

DX-3030 Handle/merge PATH case insensitively on Windows

[mitchell-as]

Test failures are known issues and unrelated to this PR.

[Naatan]

In addition to the comments, can we make sure there is a test case covering this mechanic (specifically: PATH and Path on Windows).

[Naatan]

Suggested change

	if pev.Name != osName {
	// On Windows, delete the case-insensitive version. Our case-sensitive version has already
	// processed the value of the case-insensitive version.
	delete(res, osName)
	}
	if pev.Name != osName {
	// Delete the redundant value that ours could conflict with
	// Eg. this would delete "Path" while preserving our "PATH"
	delete(res, osName)
	}