[various] Update flutter.dev links to more reliable destinations

[parlough]

Contributes to flutter/website#10363 by updating to the latest links and updating some links to use new /to/ links that can be updated as needed.

Pre-launch Checklist

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• I read the [Tree Hygiene] page, which explains my responsibilities.
• I read and followed the [relevant style guides] and ran the auto-formatter. (Unlike the flutter/flutter repo, the flutter/packages repo does use dart format.)
• I signed the [CLA].
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• I [linked to at least one issue that this PR fixes] in the description above.
• I updated pubspec.yaml with an appropriate new version according to the [pub versioning philosophy], or this PR is [exempt from version changes].
• I updated CHANGELOG.md to add a description of the change, [following repository CHANGELOG style], or this PR is [exempt from CHANGELOG changes].
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is [test-exempt].
• All existing and new tests are passing.

[stuartmorgan-g]

(Not sure if we want to land this as is, to minimize incoming conflicts, and then rely on next publishes to surface the changes, or if we want to roll versions of all of modified pkgs!)

If there's no plan to break any of these links any time soon, we can bypass versioning.

[auto-submit]

auto label is removed for flutter/packages/6963, due to - The status or check suite Linux_android android_device_tests_shard_2 master has failed. Please fix the issues identified (or deflake) before re-applying this label.

[auto-submit]

auto label is removed for flutter/packages/6963, due to - The status or check suite Mac_arm64 ios_platform_tests_shard_3 master has failed. Please fix the issues identified (or deflake) before re-applying this label.

• The status or check suite Mac_arm64 ios_platform_tests_shard_5 master has failed. Please fix the issues identified (or deflake) before re-applying this label.