Enhancement: Update Dark Mode Paradigm

[macandcheese]

Description

As a follow-up from a Teams conversation, we should explore "inverting" the dark mode paradigm to provide a better experience. Foreground colors should be lighter than background colors.

This is pretty standard across competitor design systems and seems like a good improvement.

Link to Teams meeting where this was discussed: https://teams.microsoft.com/l/message/19:fd15b51dacd24e70895ec1218a54ae06@thread.skype/1626380916800?tenantId=aee6e3c9-711e-4c7c-bd27-04f2307db20d&groupId=56fae21a-9407-4943-859f-a9bfcf0bbad3&parentMessageId=1626380916800&teamName=Calcite%20Design%20System&channelName=Calcite%20Components&createdTime=1626380916800

Relevant Info

https://material.io/design/color/dark-theme.html#properties

Would require updating calcite-colors repository with resultant changes.

[geospatialem]

~This issue is blocked awaiting creation of 863, which was included in the design phase of the new component, calcite-textarea. Prior to addressing this enhancement, the textarea component will be developed and implemented.~

This applies to a different issue and the blocked label is now removed. See #3312. cc/ @ashetland

[SkyeSeitz]

Even while retaining the same box-shadow values as light mode, similar to Material Design (note below), this could improve the box-shadow contrast with surfaces in dark mode, which is currently pretty subtle.

[geospatialem]

@SkyeSeitz With the above considerations, should we move this issue out of the freezer and consider it for a future design sprint?

[SkyeSeitz]

@geospatialem I don't believe there any issues with moving this issue out of the freezer 👍🏽 cc: @macandcheese for confirmation