Add keyboard accessibility to the New Tabs Page settings menu

[imptrx]

Description

If you go through the page you should be able to access the new tabs page settings via keyboard. The settings icon at the bottom left should be selectable.

Steps to Reproduce

1. Go to new tabs page
2. Press tab

Actual result:

The setting button will be skipped over when pressing tab but the other options will not be.

Expected result:

• The settings button should be selectable and should open the setting menu when space or enter is hit

Reproduces how often:

Always reproducible.

Test plan:

• Go to new tabs page
• Press tab
• There should be an outline when you reach the settings icon at the bottom left of the page
• Pressing space or enter will open the setting menu
• Pressing tab will allow you to select the setting menu icon again
• Pressing space or enter will open the setting menu

[imptrx]

Marked as blocked until: brave/brave-core#2857 is merged in.

[GeetaSarvadnya]

Verification passed on

Brave	0.69.115 Chromium: 76.0.3809.100 (Official Build) beta (64-bit)
Revision	ed9d447d30203dc5069e540f05079e493fc1c132-refs/branch-heads/3809@{#990}
OS	Windows 10 OS Version 1803 (Build 17134.523)

• Verified the test plan from Make NTP setting menu keyboard accessible  brave-core#2814
• Logged NTP Dashboard settings tooltip is not shown on mouse hover  #5797

Verification passed on

Brave	0.69.116 Chromium: 76.0.3809.100 (Official Build) beta (64-bit)
Revision	ed9d447d30203dc5069e540f05079e493fc1c132-refs/branch-heads/3809@{#990}
OS	Ubuntu 18.04 LTS

• Verified the test plan from Make NTP setting menu keyboard accessible  brave-core#2814
• Reproduced NTP Dashboard settings tooltip is not shown on mouse hover  #5797

Verification PASSED on macOS 10.14.6 x64 using the following build:

Brave	0.69.121 Chromium: 76.0.3809.132 (Official Build) beta (64-bit)
Revision	fd1acc410994a7a68ac25bc77513d443f3130860-refs/branch-heads/3809@{#1035}
OS	Mac OS X

• Went through verification using the outlined case under Make NTP setting menu keyboard accessible  brave-core#2814
• Reproduced & Commented on NTP Dashboard settings tooltip is not shown on mouse hover  #5797
• Found & Logged "Dashboard Settings" icon should be reselected after tabbing through the "Dashboard Settings" items #5871