Find themes built from palette maps without define-palette

Finds stylesheets whose define-light-theme or define-dark-theme takes a map of palette hues, such as primary: $orange-palette, rather than the result of define-palette, in projects that are not on Material 15 yet. The legacy components accepted such a map, while the MDC-based components of Angular Material 15 read hues that only define-palette adds, such as default, and fail the build with $color: null is not a color.