fix(multiple): change fallbacks to use m3

[andrewseguin]

When possible, use token fallbacks defined by the MDC system tokens instead of the M2 hardcoded values (or nothing).

This will affect the appearance of applications that are incorrectly lacking calls to component theme mixins, since all of these fallbacks should be ignored in favor of the fine-grained token values.

Applications that have styles changed from this should ensure that they are calling component theme mixins, e.g. mat.button-theme() if a button is used.

For example, here's the change for expansion panel expanded height:

.mat-expansion-panel-header.mat-expanded {
    // Before: 
    height: var(--mat-expansion-header-expanded-state-height);

    // After:
    height: var(--mat-expansion-header-expanded-state-height, 64px);
}

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