feat(device_info_plus): add mock

[StanleyCocos]

Description

In many scenarios, we need specific information for testing, but we can’t have all devices, so simulated data is quite necessary. I noticed that this feature was previously requested and has received significant support.

I am creating this request to add this functionality.

Related Issues

• Close [Request] device_info_plus has no setMockInitialValues #1383

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I titled the PR using Conventional Commits.
• I did not modify the CHANGELOG.md nor the plugin version in pubspec.yaml files.
• All existing and new tests are passing.
• The analyzer (flutter analyze) does not report any problems on my PR.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change (please indicate that with a ! in the title as explained in Conventional Commits).
• No, this is not a breaking change.

[miquelbeltran]

Thank you!