Rounded corners for panels on Windows show a solid background and aren't transparent

[Miyayes]

Example on Rewards panel:

Apparently this is also the case on the Contribution Banner 3.0.

[mkarolin]

Please, verify on all Desktop platforms, but on Windows both 10 and 11 need to be checked.

Test plan:

1. Start Brave
2. Join Rewards
3. Navigate to a verified publisher site
4. Open tipping banner
5. Verify that the banner's corners don't show drawing artifacts

[LaurenWags]

Removed OS/Windows and added QA/Test-All-Platforms per #30106 (comment)

[kjozwiak]

The above requires 1.52.95 or higher for 1.52.x verification 👍

[GeetaSarvadnya]

Verification PASSED on

Brave | 1.52.100 Chromium: 113.0.5672.92 (Official Build) beta (64-bit)
-- | --
Revision | b6f521170062a1fa8a82c33fb223b06fec566da1-refs/branch-heads/5672_63@{#10}
OS | Windows 10 Version 21H2 (Build 19044.2965)

• Verified the test plan from Rounded corners for panels on Windows show a solid background and aren't transparent #30106 (comment)
• BR panel rounded corner is not part of this issue, which is implemented in the issue Implement rounded corners on the Brave Rewards dropdown panel #28622, more info on slack thread https://bravesoftware.slack.com/archives/CNH9Q6REV/p1684428914002979?thread_ts=1683062994.040049&cid=CNH9Q6REV

Connected state_PASSED

Case 1: Click on BAT icon in the URL bar_PASSED

1. Clean profile 1.52.102
2. Enable rewards and connect to an custodian
3. Open brave://laurenwags.github.io and tap on the BAT icon
4. Click on Send Contribution
5. Confirmed that the tipping banner's corners are rounded and don't show drawing artifacts

Example	Example

Case 2: Click on inline tip icon_PASSED

1. Clean profile 1.52.102
2. Enable rewards and connect to an custodian
3. Open https://twitter.com/bravelaurenwags
4. Tap on the inline tip icon
5. Confirmed that the tipping banner's corners are rounded and don't show drawing artifacts

Example	Example

Grandfathered unverified state_PASSED

Case 1: Click on BAT icon in the URL bar_PASSED

1. Clean profile 1.47.x beta build
2. Enable rewards and claim UGP grants
3. Upgrade the profile to 1.52.102
4. Open brave://laurenwags.github.io
5. Click on Send Contribution
6. Confirmed that the tipping banner's corners are rounded and don't show drawing artifacts

Example	Example

Case 2: Click on inline tip icon_PASSED

1. Clean profile 1.47.x beta build
2. Enable rewards and claim UGP grants
3. Upgrade the profile to 1.52.102
4. Open https://twitter.com/bravelaurenwags
5. Click on the inline tip icon
6. Confirmed that the tipping banner's corners are rounded and don't show drawing artifacts

Example	Example

Grandfathered connected state_PASSED

Case 1: Click on BAT icon in the URL bar_PASSED

1. Clean profile 1.47.x beta build
2. Enable rewards and connect to a custodian
3. Upgrade the profile to 1.52.102
4. Open brave://laurenwags.github.io
5. Click on Send Contribution
6. Confirmed that the tipping banner's corners are rounded and don't show drawing artifacts

Example	Example

Case 2: Click on inline tip icon_PASSED

1. Clean profile 1.47.x beta build
2. Enable rewards and connect to a custodian
3. Upgrade the profile to 1.52.102
4. Open https://twitter.com/bravelaurenwags
5. Click on the inline tip icon
6. Confirmed that the tipping banner's corners are rounded and don't show drawing artifacts

Example	Example

[LaurenWags]

Removed QA/Test-All-Platforms as additional fixes for rounded corners are pending uplift to 1.52.x for #30489.

As such, the testing for #30489 will supersede this one, so #30489 is marked QA/Test-All-Platforms and will be tested once uplifted to 1.52.x.