[image_picker_android] Name picked files to match the original filenames where possible

[SynSzakala]

When picking files on Android, they are copied into cache directory. This PR ensures that names of these copied files match original names where possible, so they can be read on the dart side using XFile.name e.g. for display in the UI.
This PR also adds espresso-based native integration test for the package (currently ignored because of flutter/flutter#94748)

Part of flutter/flutter#64685.

Pre-launch Checklist

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

If you need help, consider asking for advice on the #hackers-new channel on Discord.

[stuartmorgan-g]

@GaryQian Ping on this review?

[SynSzakala]

@GaryQian @stuartmorgan Are there any additional actions required before you can review this PR?

[stuartmorgan-g]

@SynSzakala It's just waiting on @GaryQian to have time to review it. (@GaryQian ping again on this review 🙂)

[GaryQian]

@SynSzakala Let me know when you have a chance to address the review comments and I'll take another look!

[GaryQian]

@SynSzakala Did you have a chance to address the comments?

[SynSzakala]

@GaryQian Ping on this review

[stuartmorgan-g]

@GaryQian Ping on this review from triage.

[SynSzakala]

@GaryQian Cleared comments and analysis issues, resolved conflicts. Ready for review.

[stuartmorgan-g]

@reidbaker This will need a new reviewer.

[SynSzakala]

@reidbaker @stuartmorgan Are any additional steps needed to merge this? I don't have the access to add "autosubmit" label.

[auto-submit[bot]]

auto label is removed for flutter/plugins, pr: 6096, due to - Please get at least one approved review if you are already a member or two member reviews if you are not a member before re-applying this label. Reviewers: If you left a comment approving, please use the "approve" review action instead.

[auto-submit[bot]]

auto label is removed for flutter/plugins, pr: 6096, due to Validations Fail.

[stuartmorgan-g]

Since this is entirely Java changes, perhaps @camsim99 or @gmackall could do the secondary review.

[gmackall]

LGTM! Re-adding the autosubmit label.