Make quadrant chart options TypeScript types optional

[aloisklink]

📑 Summary

Make the types of the options in QuadrantChartConfig in the MermaidConfig optional. All of these (except for the values in BaseDiagramConfig) will be automatically set to their default values, so they're optional from a user perspective.

Currently, the following code will throw a TypeScript error, complaining about missing required options in QuadrantChartConfig:

mermaid.initialize({
  // throws TypeScript error
  quadrantChart: {
    chartHeight: 600,
  },
});

Resolves #4112 (comment)

📏 Design Decisions

Additionally, I've converted the config.spec.js to TypeScript, and added a test for this file (technically, this test only needs to be seen by TypeScript, we don't actually need to run it for Vitest to see anything).

Notes for reviewers

• You may find it easier to review each commit in this PR one-by-one, since GitHub's PR view can't tell that I've renamed packages/mermaid/src/config.spec.js, only the individual commit view can see it.

Pinging @subhash-halder, as they were the original author for quadrant charts, so it might be good to get a review from them too!

📋 Tasks

Make sure you

• 📖 have read the contribution guidelines
• 💻 have added unit/e2e tests (if appropriate)
  • TypeScript test added in packages/mermaid/src/config.spec.ts
• 📓 have added documentation (if appropriate)
• 🔖 targeted develop branch

[codecov]

Codecov Report

Merging #4602 (a862565) into develop (c742ac7) will decrease coverage by 0.04%.
The diff coverage is n/a.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #4602      +/-   ##
===========================================
- Coverage    79.89%   79.85%   -0.04%     
===========================================
  Files          143      143              
  Lines        16487    16487              
  Branches       518      518              
===========================================
- Hits         13172    13166       -6     
- Misses        3211     3216       +5     
- Partials       104      105       +1     

Flag	Coverage Δ
e2e	83.99% <ø> (-0.06%)	⬇️
unit	58.12% <ø> (ø)

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

Impacted Files	Coverage Δ
...aid/src/diagrams/quadrant-chart/quadrantBuilder.ts	83.92% <ø> (ø)

... and 3 files with indirect coverage changes