fix(attachment): themeing and redline

[bcalvery]

This is an update to add dark and contrast theme files for Attachment and update the styling to match redlines.

Current problems with pxToRem mean that the these changes will not render correctly until pxToRem is fixed.

Before:

After:
Default (rest / hover / focus states)

Dark (rest / hover / focus states)

High contrast (rest / hover /focus states)

[codecov]

Codecov Report

Merging #1033 into master will decrease coverage by 0.01%.
The diff coverage is 73.68%.

@@            Coverage Diff             @@
##           master    #1033      +/-   ##
==========================================
- Coverage   82.45%   82.44%   -0.02%     
==========================================
  Files         735      738       +3     
  Lines        8726     8743      +17     
  Branches     1235     1237       +2     
==========================================
+ Hits         7195     7208      +13     
- Misses       1515     1519       +4     
  Partials       16       16

Impacted Files	Coverage Δ
.../src/themes/teams-high-contrast/componentStyles.ts	100% <100%> (ø)	⬆️
...trast/components/Attachment/attachmentVariables.ts	100% <100%> (ø)
...c/themes/teams-high-contrast/componentVariables.ts	100% <100%> (ø)	⬆️
...-dark/components/Attachment/attachmentVariables.ts	100% <100%> (ø)
.../react/src/themes/teams-dark/componentVariables.ts	100% <100%> (ø)	⬆️
...kages/react/src/themes/teams-dark/siteVariables.ts	100% <100%> (ø)	⬆️
...teams/components/Attachment/attachmentVariables.ts	100% <100%> (ø)	⬆️
...contrast/components/Attachment/attachmentStyles.ts	42.85% <42.85%> (ø)
...es/teams/components/Attachment/attachmentStyles.ts	30.76% <66.66%> (+12.58%)	⬆️
... and 2 more

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