fix(VBtn): remove text colour from themed buttons
fix(VBtn): remove text colour from themed buttons

this needs to be done dynamically based on the contrast ratio

fixes #4812

Webifi/vuetify,Phlow2001/vuetify,Webifi/vuetify,Phlow2001/vuetify,Webifi/vuetify,Phlow2001/vuetify,vuetifyjs/vuetify,vuetifyjs/vuetify,vuetifyjs/vuetify,Phlow2001/vuetify,vuetifyjs/vuetify