[flutter_svg] Error handling enhancement

[minhhung2556]

Title

• Error handling when loading and parsing SVG files from anywhere.
• Expose errorBuilder to build a widget that will be shown if it fails to parse an SVG picture.

Purpose

To fix these related issues below

• adjust vector_graphics errorBuilder (to trigger on BytesLoader errors) dnfield/vector_graphics#219
• Exception: Invalid image data on preCacheImages dnfield/flutter_svg#1100
• Error found in FirebaseCrashlytics dnfield/flutter_svg#1085
• Correct error handling in custom ByteLoader dnfield/flutter_svg#1080
• Load a picture in case the given picture doesn't exists. dnfield/flutter_svg#1044
• Add errorBuilder to SvgPicture and adjust underlying vector_graphics errorBuilder (to trigger on BytesLoader errors) dnfield/flutter_svg#996
• Catching error or having an "error" placeholder dnfield/flutter_svg#1007

My related PRs at the old repositories

• Error handling enhancement dnfield/flutter_svg#1104
• Error handling enhancement dnfield/vector_graphics#258

Changes Made

• Catch error cases and return results to SVGPicture.
• Expose errorWidgetBuilder.
• Write more unit tests.
• Update example.

Testing

• Already tested by example and unit test in flutter_svg

Impact

• This change should not affect other parts of the library.

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.

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[google-cla]

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[stuartmorgan-g]

Thanks for the submission!

In the future, please do not delete the checklist that is in the PR template; it is there for a reason. This PR is missing required elements described in the checklist (I’ve restored it to the PR description), which need to be addressed before it moves forward with review.

I am marking the PR as a Draft. Please review the checklist, updating the PR as appropriate, and when that’s complete please feel free to mark the PR as ready for review.

[minhhung2556]

@stuartmorgan thanks for your advice, I've just updated it, please help me check if it is ok now.

[stuartmorgan-g]

@minhhung2556 The PR is currently failing many CI checks; you can look at Details > View more details > stdout to see what the issues are and address them.

[stuartmorgan-g]

This looks like a breaking change, so will need to be evaluated in the context of flutter/flutter#157626

If the decision there is (as I hope) to start using semver for vector_graphics*, this would need to be versioned accordingly, or would need a non-breaking alternative.

[jonahwilliams]

Rather than making it null, we can throw/catch an exception I think.

[minhhung2556]

@minhhung2556 The PR is currently failing many CI checks; you can look at Details > View more details > stdout to see what the issues are and address them.

I think it failed because of this commit: 9672f24

Regarding your review, I think I need to separate into 2 PRs: 1 for vector_graphics and 1 for flutter_svg

This looks like a breaking change, so will need to be evaluated in the context of flutter/flutter#157626

If the decision there is (as I hope) to start using semver for vector_graphics*, this would need to be versioned accordingly, or would need a non-breaking alternative.