fix(dialogs): themeing support for Teams dark and hc

[codepretty]

Fixes #1313.

This does not include all the redline work for Dialogs. This is just to fix the Dialog's color support in Teams dark and Teams high contrast themes.

Screenshots below (Before | After)
Teams theme

Teams dark theme

Teams high contrast theme

[codecov]

Codecov Report

Merging #1297 into master will decrease coverage by 0.1%.
The diff coverage is 0%.

@@            Coverage Diff            @@
##           master   #1297      +/-   ##
=========================================
- Coverage    72.3%   72.2%   -0.11%     
=========================================
  Files         764     769       +5     
  Lines        5769    5777       +8     
  Branches     1688    1712      +24     
=========================================
  Hits         4171    4171              
- Misses       1592    1600       +8     
  Partials        6       6

Impacted Files	Coverage Δ
...src/themes/teams/components/Dialog/dialogStyles.ts	0% <0%> (ø)
...high-contrast/components/Dialog/dialogVariables.ts	0% <0%> (ø)
...es/teams-dark/components/Dialog/dialogVariables.ts	0% <0%> (ø)
.../themes/teams/components/Dialog/dialogVariables.ts	0% <0%> (ø)
...ms-high-contrast/components/Dialog/dialogStyles.ts	0% <0%> (ø)

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[miroslavstastny]

Just one comment added, other than that 👍