fix(VTextarea): replace mask with clip-path

[khoanguyn1411]

Description

Fixed #21283

Replace the mask with a clip-path for more flexible width handling, as we need to exclude the scrollbar's width from the clip-path to ensure the top arrow remains visible.

Result:

Markup:

<template>
  <v-app>
    <v-container>
      <v-textarea
        label="Textarea Label"
        model-value="1
          2
          3
          4
          5
          6
          7
          8
          9
          10"
      />
    </v-container>
  </v-app>
</template>