fix(VBtn): card-actions add margin-inline-start only for for direct btns

[yuwu9145]

Description

fixes #20239

Breaking change: v-card-actions only impacts its immediate child v-btns

Markup:

<template>
  <v-app>
    <v-container>
      <v-number-input control-variant="stacked" />
    </v-container>
    <v-card-actions>
      <v-btn text="one" />
      <v-btn text="two" />
    </v-card-actions>
    <v-card-actions>
      <v-number-input control-variant="stacked" />
    </v-card-actions>
  </v-app>
</template>

[yuwu9145]

@KaelWD Does this look like a breaking change to you? Might need to rebase to dev

[KaelWD]

It provides slim: true and variant: 'text' to non-direct children too so the old description is more correct. I think we could also use gap here instead of margin.