Add additional padding to new tab "+" button

[rebron]

Description

Tabs, specifically the close button, and the "new tab" button are close together and could use additional padding/separation to improve closing a tab or selecting a new tab by mistake.

Other browsers like Chrome and Yandex have slightly bigger padding and separation between buttons.

Steps to Reproduce and Actual Result:

Noticeable with a new window and notice spacing between a tab's close button and the new tab icon.

Expected result:

[placeholder for design] @karenkliu

Reproduces how often:

Easy

Brave version (brave://version info)

All.

Version/Channel Information:

• Can you reproduce this issue with the current release? yes
• Can you reproduce this issue with the beta channel? yes
• Can you reproduce this issue with the nightly channel? yes

Other Additional Information:

• Does the issue resolve itself when disabling Brave Shields? n/a
• Does the issue resolve itself when disabling Brave Rewards? n/a
• Is the issue reproducible on the latest version of Chrome? no

Miscellaneous Information:

[bsclifton]

Added missing milestone

[stephendonner]

Verified using inline testplan on

Brave	1.21.44 Chromium: 88.0.4324.146 (Official Build) beta (x86_64)
Revision	406dc88511162d6598242f2c709be1414a042fb0-refs/branch-heads/4324@{#2088}
OS	macOS Version 11.2 (Build 20D64)

In addition to the increased horizontal margin padding between tab-close (X) and open new tab (+), I checked:

• hover states
• click states

1.19.92	1.21.44

---

Verification passed on

Brave	1.21.52 Chromium: 88.0.4324.152 (Official Build) dev (64-bit)
Revision	6579930fc53b4dc589c042bec9d0a3778326974d-refs/branch-heads/4324@{#2106}
OS	Ubuntu 18.04 LTS

Verified test plan from the description. Verified hover and click states

1.20.103	1.21.52

---

Verification passed on

Brave | 1.21.56 Chromium: 88.0.4324.152 (Official Build) dev (64-bit)
-- | --
Revision | 6579930fc53b4dc589c042bec9d0a3778326974d-refs/branch-heads/4324@{#2106}
OS | Windows 10 OS Version 2004 (Build 19041.804)

Verified the spacing additional padding to new tab "+" button

1.20.x Vs 1.21.x