Browser-laptop: Refactor textarea with Aphrodite into TextArea

[luixxiul]

Test Plan

1. Open about:adblock
2. Input some strings inside the textarea
3. Make sure the font size is set to 14.5px
4. Make sure 10px margins exist on the top and the bottom of the textarea
5. Open about:styles
6. Make sure <TextForm> and <DefaultTextForm> are correctly displayed

Original issue details

Describe the issue you encountered:
https://github.com/brave/browser-laptop/issues/6851#issuecomment-275051821

The font-size should be 14.5px based on https://github.com/brave/browser-laptop/pull/6689/files#diff-fa59d1e0221a5bee94fd2abd9b96dcfdR17

Also the textarea should be updated to an Aphrodite component. And I'm creating it.

• Extra QA steps:
  1.
  2.
  3.

• Any related issues: https://github.com/brave/browser-laptop/pull/7152/files#diff-4d41992378b9b0e8b0546117c1668299R131 of #7152

[luixxiul]

I will also create <SyncTextArea> based on https://github.com/brave/browser-laptop/pull/7152/files#diff-4b50ff14dadc9756719a577a72f520d6R1562 / CC: @ayumi

[luixxiul]

I added <SyncTextArea> with 864f5611d6f834ad78bf112b38881d844158e291. It is based on 4a8bd86 of #7165.

I will create an PR after #7165 is merged.

[bsclifton]

Looks nice! Great work, @luixxiul 😄

[cezaraugusto]