[native_toolchain_c] Fix Windows env quoting in runProcess (#3321)

[Chaos02]

On Windows, runProcess launched the subprocess with runInShell: true whenever a workingDirectory was supplied. The shell re-parsed every entry in the supplied environment map, so values containing spaces or quotes (common for PATH, INCLUDE, LIB entries from MSVC environment batch files) were corrupted before reaching the child process.

This PR:

• Drops runInShell unconditionally — the child now receives environment verbatim from dart:io's Process.start.
• Adds _quoteForCommandLog, which quotes env values containing whites

Related Issues

Fixes #3321

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[dcharkes]

This PR seems similar to #3323, but this is about env vars instead of the executable path.

As discussed in that PR, we had issues before with invoking tools on Windows, and that's why the runInShell was added. We can try removing it, but it might lead to those issues returning. Is there a way to make it work without changing runInShell? Or is removing runInShell the only fix?

[github-actions]

Package publishing

Package	Version	Status	Publish tag (post-merge)
package:code_assets	1.0.0	already published at pub.dev
package:data_assets	0.19.6	already published at pub.dev
package:ffi	2.2.0	already published at pub.dev
package:hooks	1.0.3	already published at pub.dev
package:hooks_runner	1.2.1	already published at pub.dev
package:jni_flutter	1.0.1	already published at pub.dev
package:native_toolchain_c	0.18.1	ready to publish	native_toolchain_c-v0.18.1
package:record_use	0.6.1-wip	WIP (no publish necessary)
package:swift2objc	0.2.0-wip	WIP (no publish necessary)
package:swiftgen	0.1.2	already published at pub.dev

Documentation at https://github.com/dart-lang/ecosystem/wiki/Publishing-automation.

[github-actions]

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Package	Change	Current Version	New Version	Needed Version	Looking good?
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