feat(Header): introduce 'color' variable

[kuzhelov]

Header color

Introduce color property to Header and Header.Description

TODO

• Conformance test
• Minimal doc site example
• Stardust base theme
• Teams Light theme
• Teams Dark theme
• Teams Contrast theme
• Confirm RTL usage
• W3 accessibility check
• Stardust accessibility check
• Update glossary props table
• Update the CHANGELOG.md

API Proposal

Header - color (variable)

Defines color of Header.

<Header variables={{ color: 'red' }} content="..." />

---

Header.Description - color (variable)

Defines color of header's description (Header.Description).

<Header ... >
   <Header.Description variables={{ color: 'red' }} content='...' />
</Header>

[codecov]

Codecov Report

Merging #72 into master will increase coverage by 0.07%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #72      +/-   ##
==========================================
+ Coverage   85.89%   85.97%   +0.07%     
==========================================
  Files          74       76       +2     
  Lines        1106     1112       +6     
  Branches      219      228       +9     
==========================================
+ Hits          950      956       +6     
  Misses        149      149              
  Partials        7        7

Impacted Files	Coverage Δ
src/components/Header/headerVariables.ts	100% <100%> (ø)
...rc/components/Header/headerDescriptionVariables.ts	100% <100%> (ø)
...teams/components/Header/headerDescriptionStyles.ts	100% <100%> (ø)	⬆️
src/themes/teams/components/Header/headerStyles.ts	100% <100%> (ø)	⬆️
src/components/Header/HeaderDescription.tsx	100% <100%> (ø)	⬆️
src/components/Header/Header.tsx	95.65% <100%> (+0.41%)	⬆️

---

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[mnajdova]

Is it necessary to add the variables prop? We don't have it added in any of the other components.

[kuzhelov]

actually, this thing turns out to be necessary for the sake of preventing variables being passed further to the child DOM tree - otherwise we can end up with the following thing:

For the sake of preventing this to happen the variables property has been declared as handled.

[mnajdova]

Got it! We should address this in the other components as well. Approving this PR.