[flutter_markdown] Added height and width to image builder

[M97Chahboun]

• Adds height & width to imageBuilder.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki 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.
• 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.

[domesticmouse]

I'm curious how image height and width are parsed from the markdown.

[M97Chahboun]

@domesticmouse
If you means how markdown parse the h & w of image
check this line
parsed by get height and width from this format imageLink#200x200

[domesticmouse]

Please add a test that covers width x height from markdown to final usage to prevent future breakage

[stuartmorgan]

• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]

This was not done; please don't check boxes without completing the steps they describe.

• All existing and new tests are passing.

CI indicates that the new test is not passing, which will need to be resolved before this can be reviewed.

[domesticmouse]

What happens if width and height are not specified?

[M97Chahboun]

Yes is same test result
I will remove it

[M97Chahboun]

I run image tests before any changes and I get :

══╡ EXCEPTION CAUGHT BY FLUTTER TEST FRAMEWORK ╞════════════════════════════════════════════════════
The following assertion was thrown while running async test code:
Golden "assets/images/golden/image_test/resource_asset_logo.png": Pixel test failed, 0.00% diff
detected.
Failure feedback can be found at
/Users/user/Development/packages/packages/flutter_markdown/test/failures

When the exception was thrown, this was the stack:
#0      LocalFileComparator.compare (package:flutter_test/src/_goldens_io.dart:106:5)
<asynchronous suspension>
#1      MatchesGoldenFile.matchAsync.<anonymous closure> (package:flutter_test/src/_matchers_io.dart:118:32)
<asynchronous suspension>
<asynchronous suspension>
(elided one frame from dart:async)

The exception was caught asynchronously.
════════════════════════════════════════════

Any advise please