Tipping Banner should be more accessible

[ryanml]

The following updates should be made:

1. Banner must receive focus upon opening.
2. ESC key must close banner.
3. Choice A button for BAT tip amount must be pre-selected upon banner open.
4. "SEND TIP" button changes shape as shown.
5. "SEND TIP" button is pre-focused so that RETURN key executes send action and closes banner window.
6. ALL 4 buttons present in this panel are set to receive focus for accessibility when tabbing through action elements.
7. Update default text to reflect copy shown in photo.

[NejcZdovc]

@davidtemkin I would go with mid option and not with lower option by default

[LaurenWags]

Questions have been added to the spec for @mandar-brave @alexwykoff to address in regards to item 3 and 7 from description.

[LaurenWags]

Verified passed with

Brave	1.1.4 Chromium: 78.0.3904.97 (Official Build) beta (64-bit)
Revision	021b9028c246d820be17a10e5b393ee90f41375e-refs/branch-heads/3904@{#859}
OS	macOS Version 10.13.6 (Build 17G5019)

• Confirmed the banner receives focus upon opening.
• Confirmed ESC key closes the banner (when banner is in focus)
• Confirmed Choice B button for BAT tip amount is pre-selected upon banner open (per Tipping Banner should be more accessible #6147 (comment) )
• Confirmed Send Tip button has same shape as image in description.
• Confirmed when user has enough BAT to cover the tip preselected in Choice B, the Send Tip button is pre-focused and the return key executes send action and closes banner window. However, if you do not have enough BAT, there is no indication of what is in focus on the banner. Logged unclear what is focused on Tip banner when not enough BAT - follow up to 6147 #6985 for this. Could be related to Set Contribution button border/edge is shown when wallet balance is zero #6914 for monthly contribution banner.
• Confirmed all buttons present in this panel are set to receive focus for accessibility when tabbing through action elements. However, I did encounter and log Tipping Banner needs better keyboard accessibility - Follow up to 6147 #6986 for this. Once you tab away from Send Tip you are taken out of the banner and unable to return to the banner without clicking inside the banner with the mouse.
• Confirmed the default text was updated to reflect copy shown in image in description.

* Confirmed custom banners still display as expected.

Verification passed on

Brave	1.1.4 Chromium: 78.0.3904.97 (Official Build) beta (64-bit)
Revision	021b9028c246d820be17a10e5b393ee90f41375e-refs/branch-heads/3904@{#859}
OS	Windows 10 OS Version 1803 (Build 17134.1006)

• Confirmed the banner receives focus upon opening.
• Confirmed ESC key closes the banner (when banner is in focus)
• Confirmed Choice B button for BAT tip amount is pre-selected upon banner open (per Tipping Banner should be more accessible #6147 (comment) )
• Confirmed Send Tip button doesn't aligned with other buttons mentioned in the description logged (Send Tip alignment issue in beta build 0.72.x #6915)
• Confirmed when user has enough BAT to cover the tip preselected in Choice B, the Send Tip button is pre-focused and the return key executes send action and closes banner window. However, if you do not have enough BAT, there is no indication of what is in focus on the banner. Encountered unclear what is focused on Tip banner when not enough BAT - follow up to 6147 #6985 for this.
• Confirmed all buttons present in this panel are set to receive focus for accessibility when tabbing through action elements. encountered Tipping Banner needs better keyboard accessibility - Follow up to 6147 #6986
• Confirmed the default text was updated to reflect copy shown in image in description.
  
• Confirmed custom banners still display as expected.
  

Verification passed on

Brave	1.1.4 Chromium: 78.0.3904.97 (Official Build) beta (64-bit)
Revision	021b9028c246d820be17a10e5b393ee90f41375e-refs/branch-heads/3904@{#859}
OS	Ubuntu 18.04 LTS

• Confirmed the banner receives focus upon opening.
• Confirmed ESC key closes the banner (when banner is in focus)
• Confirmed Choice B button for BAT tip amount is pre-selected upon banner open (per Tipping Banner should be more accessible #6147 (comment) )
• Confirmed Send Tip button doesn't aligned with other buttons mentioned in the description logged (Send Tip alignment issue in beta build 0.72.x #6915)
• Confirmed when user has enough BAT to cover the tip preselected in Choice B, the Send Tip button is pre-focused and the return key executes send action and closes banner window. However, if you do not have enough BAT, there is no indication of what is in focus on the banner. Encountered unclear what is focused on Tip banner when not enough BAT - follow up to 6147 #6985 for this.
• Confirmed all buttons present in this panel are set to receive focus for accessibility when tabbing through action elements. encountered Tipping Banner needs better keyboard accessibility - Follow up to 6147 #6986
• Confirmed the default text was updated to reflect copy shown in image in description.
  
• Confirmed custom banners still display as expected.