Shift-enter to add newline and support IME inputs

[nullhook]

No description provided.

[stephendonner]

Verification PASSED using

Brave | 1.62.69 Chromium: 119.0.6045.163 (Official Build) nightly (x86_64)
-- | --
Revision | 271270f8302c71e63d6cca16eee5578836d3fd96
OS | macOS Version 14.2 (Build 23C5047e)

Shared Steps:

1. install 1.62.69
2. launch Brave
3. click on Leo in the sidebar
4. click Accept and begin

tab to focus/select the Send message to Leo icon - PASSED

Confirmed pressing tab repeatedly walks the DOM

Confirmed pressing spacebar or return/enter submitted the message

example	example	example

shift+return - PASSED

Confirmed pressing shift + return in the Enter a prompt here textfield added a newline

return - PASSED

Confirmed pressing return sent the message

example	example	example

[LaurenWags]

@nullhook @rebron could one of you please add release-notes/exclude or release-notes/include label as appropriate for this one? Thanks!

[GeetaSarvadnya]

@nullhook This accessibility issue implemented for Android as well? If so, please add the test plan. Thanks!

The shortcut keys Tab Spacebar and Return are available only on Desktop I am not sure how to test this issue on Android.
cc: @kjozwiak @hffvld @Uni-verse

[hffvld]

Verified on Pixel 7 using version(s):

Device/OS: Pixel 7 / panther_beta-user 14 AP11.231020.013.A1 release-keys
Brave build: 1.62.128
Chromium: 120.0.6099.144 (Official Build) beta (64-bit) 

Filed follow-up issue #35104

STEPS:

1. Connect a physical keyboard to the device
2. Launch Brave
3. Three-dot menu > Leo
4. Tap Accept and begin
5. Use Tab on the keyboard to focus/select the text field and type a query
6. Use Tab to focus/select the Send message to Leo icon > Verify
7. Use Spacebar or Enter to submit the message > Verify
8. Use Tab to focus/select the text field again > Type a query
9. Use Shift + Enter to add new line > Verify

ACTUAL RESULTS:

• Verified that pressing Tab repeatedly walks the DOM
• Verified that pressing Spacebar or Enteris submitting the message to Leo
• Verified that pressing Shift + Enter must add new line in the text field

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2024-01-03_10-03-31.mp4

[kjozwiak]

Removing the above from #35625 as Leo is targeting 1.63.x for Android.