[SG-39285] Remove style duplication caused by the forkedBranded.scss file

Created by: gitstart-sourcegraph

Descriptions

• Move forkedBranded.scss file in favor of the branded.scss import

Refs

Sourcegraph Issue GitStart Issue

Implimentation details

• Rename client/branded/src/global-styles/index.scss to client/branded/src/global-styles/base.scss
• Move @import './highlight'; from base.scss to client/branded/src/global-styles/index.scss
• client/vscode/src/webview/index.scss should import client/branded/src/global-styles/base.scss instead of forkedBranded.scss
• All style changes specific to the VSCode theme should be made in the client/vscode/src/webview/index.scss

Test plan

• The details above should be implemented
• The changes are vscode extension, just check if there no UI changes

App preview:

• Web
• Storybook

Check out the client app preview documentation to learn more.