feat: Add WrapperExtension helper

[Sub6Resources]

Fixes #1262

[codecov]

Codecov Report

Patch coverage: 94.64% and project coverage change: +0.56 🎉

Comparison is base (8ac444b) 57.16% compared to head (e467e3f) 57.73%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1264      +/-   ##
==========================================
+ Coverage   57.16%   57.73%   +0.56%     
==========================================
  Files          36       37       +1     
  Lines        2610     2645      +35     
==========================================
+ Hits         1492     1527      +35     
  Misses       1118     1118              

Impacted Files	Coverage Δ
lib/src/builtins/details_element_builtin.dart	11.11% <0.00%> (ø)
lib/src/builtins/image_builtin.dart	60.39% <ø> (ø)
lib/src/builtins/ruby_builtin.dart	92.06% <ø> (ø)
lib/src/builtins/text_builtin.dart	95.83% <ø> (ø)
lib/src/extension/helpers/image_extension.dart	0.00% <0.00%> (ø)
lib/src/extension/helpers/image_tap_extension.dart	0.00% <0.00%> (ø)
lib/src/extension/helpers/matcher_extension.dart	53.84% <ø> (ø)
lib/src/extension/helpers/tag_extension.dart	58.33% <ø> (ø)
lib/src/extension/html_extension.dart	81.25% <ø> (ø)
...ackages/flutter_html_svg/lib/flutter_html_svg.dart	87.39% <ø> (ø)
... and 5 more

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[Sembauke]

It might be hard for the user to know what the difference is between a TagExtension and a WrapperExtension class. Because they basically do the same thing?

[Sub6Resources]

Fair. I can add some more documentation. Essentially the TagExtension is for providing a custom widget in place of a tag. For example, rendering all <flutter> tags as a FlutterLogo widget. The WrapperExtension is for wrapping any instance of a tag inside of another widget, while still rendering the tag using the built-in tag support or other extensions.

Would naming like WrapTagExtension be clearer?

[Sembauke]

Yes, I think WrapTagExtension would make things a bit more clear. But I also think there should be some good documentation on what the differences are. Keep them close in the example too.

[Sub6Resources]

I just renamed the Extension and added a bit more documentation.

Some of the documentation is yet to come in the form of the wiki: https://github.com/Sub6Resources/flutter_html/wiki/How-To-Use-Extensions. Sorry my documentation isn't super flushed out yet!

[Sembauke]

No worries, I am only pointing these things out cause I am trying to help and make it better!