Add support for dynamic string attributes in vdom and add deprecation…

[DylanPiercey]

Description

Adds back and deprecates support for passing a string as dynamic attributes in the vdom (improved Marko v3 Compatibility).

Checklist:

• I have read the CONTRIBUTING document and have signed (or will sign) the CLA.
• I have updated/added documentation affected by my changes.
• I have added tests to cover my changes.

[codecov]

Codecov Report

Merging #1378 into master will increase coverage by <.01%.
The diff coverage is 94.44%.

@@            Coverage Diff             @@
##           master    #1378      +/-   ##
==========================================
+ Coverage   90.58%   90.59%   +<.01%     
==========================================
  Files         344      344              
  Lines       12483    12501      +18     
==========================================
+ Hits        11308    11325      +17     
- Misses       1175     1176       +1

Impacted Files	Coverage Δ
src/runtime/html/helper-attrs.js	100% <100%> (ø)	⬆️
src/runtime/vdom/helper-attrs.js	96.42% <93.33%> (-3.58%)	⬇️

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[coveralls]

Coverage increased (+0.006%) to 90.593% when pulling a578bce on dynamic-str-attrs-vdom into cb4935a on master.