fix(material/core): add optional warning for incomplete themes

[andrewseguin]

Add a flag that can be transformed to "true" internally that produces an error if users call a theming function with an incomplete map.

For example, calling mat.button-typography($theme) that doesn't have typography will error.

Another example, calling mat.button-theme($theme) without color, typography, and density will error.

For cases where users do not want to include certain styles, e.g. typography, they should directly call "-color()" and "-density()" and skip "-typography()"

The intent of this is to standardize theming configurations internally so that all apps explicitly declare what they want to include in their theming, making it more clear what they are not including as well. All apps will default to typography: null or density: 0 if it is missing in their theme config

[devversion]

Nice

[crisbeto]

LGTM

[angular-automatic-lock-bot]

This issue has been automatically locked due to inactivity.
Please file a new issue if you are encountering a similar or related problem.

Read more about our automatic conversation locking policy.

_{This action has been performed automatically by a bot.}