Implement keyboard shortcut for private tab and private tab with Tor

[srirambv]

Description

Implement keyboard shortcut for private tab and private tab with Tor

Expected result:

mac
Cmd+Shift+P for Private tab using Tor
Cmd+Shift+N for Private tab not using Tor

Windows/Linux
Ctrl+Shift+P for Private tab using Tor
Ctrl+Shift+N for Private tab not using Tor

[riastradh-brave]

Ctrl-Shift-P/Cmd-Shift-P is taken for printing. We settled on Alt-Shift-N/Cmd-Opt-N for new private window with Tor for now in #1387.

[srirambv]

Verification Passed on

Brave	0.55.17 Chromium: 70.0.3538.67 (Official Build) (64-bit)
Revision	9ab0cfab84ded083718d3a4ff830726efd38869f-refs/branch-heads/3538@{#1002}
OS	Linux

• Verified Ctrl+Shift+N opens a new private window
• Verified Alt+Shift+N opens a new Tor window (based on Menu items & keyboard shortcuts to launch private windows with Tor #1387 )

Verified passed with

Brave	0.55.17 Chromium: 70.0.3538.67 (Official Build) (64-bit)
Revision	9ab0cfab84ded083718d3a4ff830726efd38869f-refs/branch-heads/3538@{#1002}
OS	Mac OS X

• Verified Cmd+Shift+N opens a new private window
• Verified Cmd+Option+N opens a new Tor window

Verification Passed on

Brave	0.55.17 Chromium: 70.0.3538.67 (Official Build) (32-bit)
Revision	9ab0cfab84ded083718d3a4ff830726efd38869f-refs/branch-heads/3538@{#1002}
OS	Windows

• Verified Ctrl+Shift+N opens a new private window
• Verified Alt+Shift+N opens a new Tor window (based on Menu items & keyboard shortcuts to launch private windows with Tor #1387 )