[analyzer] Add quick fix for sort_pub_dependencies lint

[nathannewyen]

Adds a quick fix that sorts dependencies alphabetically in pubspec.yaml when the sort_pub_dependencies lint is triggered.

Changes

• Added sortDependencies FixKind
• Implemented _sortPubDependencies() in PubspecFixGenerator
• Added tests

Fixes #47958

[copybara-service]

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[mraleph]

@nathannewyen if you are still working on this please address comments that reviewer has left on Gerrit. Otherwise please close PR.

[mraleph]

Seems stale. If you decide to return to this - please ping us.