feat(theme): Allow overriding of text themes

[gline9]

When theme colors are very close to the border of light vs dark theme, the chosen text color can be different that what you want. Currently there is no way to change which text theme was chosen for a particular color. This can be accomplished by adding the !default tag to the chosen theme and allowing the variable to be overridden similarly to how the theme colors can be.

[codecov]

Codecov Report

Merging #299 into master will not change coverage.
The diff coverage is n/a.

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  Hits         4241     4241           
  Misses        412      412

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[trimox]

Hey @gline9 Thanks for your PR! Developers would appreciate the flexibility to customize the tone colors.

The tone variables were implemented to compute a minimum contrast ratio to ensure color blind user accessibility. I also understand the MDC team has no plans to allow developers to alter these variables.

Long and short, our current process to sync upstream Sass changes is to re-import all the Sass from material-components-web into src/theme/material-components-web. Re-importing means the changes in _variables.scss would be lost.

Currently we extend the Sass of material-components-web using src/theme/material.scss and src/theme/extend. However; this approach would not work either.

I'm open to feedback regarding re-importing of upstream Sass files! 😄
Thanks again,
-trimox

[trimox]

Closing. PR exists upstream: material-components/material-components-web#1481