Improve toolchain text

[timsneath]

Description

Address confusion over Windows dependencies by adding indentation and improving text language to flutter doctor.

Related Issues

#44184

Tests

I added the following tests:

Checklist

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• I read the Contributor Guide and followed the process outlined there for submitting PRs.
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• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I updated/added relevant documentation (doc comments with ///).
• All existing and new tests are passing.
• The analyzer (flutter analyze --flutter-repo) does not report any problems on my PR.
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Breaking Change

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• Yes, this is a breaking change. If not, delete the remainder of this section.
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[fluttergithubbot]

It looks like this pull request may not have tests. Please make sure to add tests before merging. If you need an exemption to this rule, contact Hixie.

Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing.

[googlebot]

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[googlebot]

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