Increase size of hover indication and clickable area for New Tab button

[bradleyrichter]

Our current New (+) button is noticeably smaller than chrome which may be causing some usability issues.

The style will not be negatively effected if we make the clickable area larger.

Current compared to chrome (shown as overlay circle)

New size to improve usability of click region:

Assuming the squircle is based on a center point, enlarging it from 20px to 28px should work.

[stephendonner]

Verified PASSED using

Brave	1.41.55 Chromium: 102.0.5005.115 (Official Build) nightly (x86_64)
Revision	174dbe6e33bc81994fceb71d751be201d0b4803d-refs/branch-heads/5005_109@{#3}
OS	macOS Version 12.5 (Build 21G5037d)

Visually inspected and compared default and hover states between 1.41.55 and 1.39.120.

Confirmed larger hover region.

Dark theme/mode

	1.41.55	1.39.120
default
hover

Light theme/mode

	1.41.55	1.39.120
default
hover