Enable split view in nightly by default

[simonhong]

fix brave/brave-browser#38710

[github-actions]

✅ Test Seed Generated Successfully

To apply the test seed:

1. Desktop: Launch the browser with --variations-pr=1296.
   Android: Set the command line to --variations-pr=1296 in debug menu, restart the browser.
   iOS: Set Variations PR to 1296 in Brave Core Switches debug menu, restart the browser.
2. Wait 5-10 seconds to fetch the seed.
3. Restart the browser to apply the seed.
4. Ensure Active Variations section at brave://version starts with the expected seed version (see below).

Seed Details

Parameter	Value
Version	pull/1296@79043514ae874adeaf177ee3551150e126bf6107
Uploaded	Wed, 22 Jan 2025 00:13:57 GMT
PR commit	36a6548
Base commit	daf6d93
Merge commit	7904351
Serial number	cec361bbb1b231054121d98c6ab9bd77

[simonhong]

Set as draft as min version should be updated after merging brave/brave-core#24478
cc @rebron

[kjozwiak]

Quick Note: The following basically ensures that the Griffin study is working as expected. The feature was already verified by QA via the 1.76.x milestone as Split Screen is currently set to be released via 1.76.x. However, this could change.

Nightly verification:

Test Case #1 - BraveSplitViewStudy:Enabled

Verification PASSED on Win 11 Pro x64 using the following build(s):

Brave | 1.76.31 Chromium: 132.0.6834.83 (Official Build) nightly (64-bit)
-- | --
Revision | 58fb0f04c59a55fa402ef190a47567d6ecb8367c
OS | Windows 11 Version 24H2 (Build 26100.2605)

• launched 1.76.31 Chromium: 132.0.6834.83 using the following
  • brave.exe --enable-logging=stderr --variations-pr=1296
• restarted 1.76.31 Chromium: 132.0.6834.83
• ensured pull/1296@79043514ae874adeaf177ee3551150e126bf6107 via brave://version
• ensured that BraveSplitViewStudy:Enabled was appearing under brave://version
• ensured that Split screen is being enabled/usable without any obvious issues

`Example	Example

Test Case #2 - BraveSplitViewStudy (doesn't meet min_version requirement)

Verification PASSED on Win 11 Pro x64 using the following build(s):

Brave | 1.76.28 Chromium: 132.0.6834.83 (Official Build) nightly (64-bit) 
--- | ---
Revision | 2e2acbc08f62224f09450d93311a757a9b96470f
OS | Windows 11 Version 24H2 (Build 26100.2605)

• launched 1.76.28 Chromium: 132.0.6834.83 using the following
  • brave.exe --enable-logging=stderr --variations-pr=1296
• restarted 1.76.28 Chromium: 132.0.6834.83
• ensured pull/1296@79043514ae874adeaf177ee3551150e126bf6107 via brave://version
• ensured that BraveSplitViewStudy doesn't appear under brave://version due to not meeting the min_version requirement

`Example	Example

[kjozwiak]

Uplift into production/main approved after deliberating with @brave/uplift-approvers.