refactor: migrate to Sass module system (wip)

[jathak]

DO NOT MERGE. This PR is just designed to demonstrate the result of the migration script and discuss the changes that are necessary.

This PR was generated by running this script on top of #5337. It migrates most components (excluding chips, select, and textfield) to the Sass module system, removing manual mdc-$component prefixes and implicit dependencies between files (though still leaving both intact for users still using @import).

The Sass migrator focuses on correctness and the API that each files exposes, so the code it outputs may not always conform to your preferred style. In most cases, those style changes should be applied on top of the migrator's output, but if there's something style-related that you think it makes sense for the migrator to handle, we could add that support.

Changes to the general structure of the code after migration will require changes to the script, which should then be re-run on top of master.

High-level overview of the changes made here:

• Prefixes (e.g. mdc-button-) for each component have been removed from all variables, functions, and mixins within the code. Prefixes on CSS selectors are unaffected.
• When depending on one of a component's partial files via @use, only members directly declared in that file are available.
• The non-partial files for components that have them do forward members from their own partials, but not from other components (so mdc-button.scss exposes the button mixins, but not the theme mixins, for example)
• Import-only files have been generated that add back all of the prefixes and explicitly forward all members that were implicitly available via @import previously, so existing users that still use @import shouldn't break as a result of these changes. These files will then be used by the migrator when those users later migrate to the module system themselves.

[codecov-io]

Codecov Report

Merging #5354 into master will increase coverage by 0.97%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #5354      +/-   ##
==========================================
+ Coverage   96.34%   97.31%   +0.97%     
==========================================
  Files         163      164       +1     
  Lines        6260     6257       -3     
  Branches      834      781      -53     
==========================================
+ Hits         6031     6089      +58     
+ Misses        229      168      -61

Impacted Files	Coverage Δ
packages/mdc-textfield/constants.ts	100% <ø> (ø)	⬆️
packages/mdc-textfield/component.ts	97.95% <ø> (-0.07%)	⬇️
packages/mdc-switch/component.ts	30.35% <0%> (-61.17%)	⬇️
packages/mdc-notched-outline/component.ts	60.71% <0%> (-35.84%)	⬇️
testing/dom/events.ts	71.42% <0%> (-28.58%)	⬇️
packages/mdc-switch/foundation.ts	97.29% <0%> (-2.71%)	⬇️
packages/mdc-line-ripple/foundation.ts	100% <0%> (ø)	⬆️
packages/mdc-floating-label/component.ts	100% <0%> (ø)	⬆️
... and 9 more

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