Added functionality to support style keyword

[jgreywolf]

📑 Summary

This change allows users to use syntax such as:

style CLASSNAME fill:#000,stroke:2px

in order to apply css styles to individual class boxes

Resolves #2408

Example

Rendering the following Mermaid diagram will look like:

```mermaid
 classDiagram 
   class Animal 
   class Mineral 
   style Animal fill:#f9f,stroke:#333,stroke-width:4px 
   style Mineral fill:#bbf,stroke:#f66,stroke-width:2px,color:#fff,stroke-dasharray: 5 5 
```

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[sidharthv96]

The doc change is mandatory. Rest are good to have.

[codecov]

Codecov Report

Merging #5111 (2b4940d) into develop (6e64556) will decrease coverage by 2.58%.
The diff coverage is 55.55%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #5111      +/-   ##
===========================================
- Coverage    79.37%   76.80%   -2.58%     
===========================================
  Files          166      166              
  Lines        13878    13886       +8     
  Branches       705      707       +2     
===========================================
- Hits         11016    10665     -351     
- Misses        2710     3059     +349     
- Partials       152      162      +10     

Flag	Coverage Δ
e2e	81.96% <55.55%> (-3.23%)	⬇️
unit	43.04% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
packages/mermaid/src/dagre-wrapper/nodes.js	78.36% <ø> (-11.26%)	⬇️
...ges/mermaid/src/diagrams/class/classRenderer-v2.ts	79.85% <100.00%> (ø)
packages/mermaid/src/diagrams/class/classTypes.ts	93.47% <ø> (ø)
packages/mermaid/src/diagrams/class/classDb.ts	81.18% <50.00%> (+7.99%)	⬆️

... and 22 files with indirect coverage changes

[aloisklink]

Love this new feature!

The doc change is mandatory. Rest are good to have.

Also, please add a full example + screenshot to your PR description, because this feature looks beautiful, and you should show it off to other mermaid users that see this PR!

[aloisklink]

Looks good to me! We did have a failing E2E test, but I think it might just be a flaky test, so I've rerun the tests and hopefully that would fix it.

[mbtools]

Thank you, Justin! The world much appreciates your effort 👍