vsce: update selection background color for default light theme

Created by: abeatrix

Close https://github.com/sourcegraph/sourcegraph/issues/35767

As reported by a user in https://github.com/sourcegraph/sourcegraph/issues/35767, there is a color conflict between the highlighted word and highlighted background in our suggestion widget that makes the highlighted suggestion unreadable in Light & Light+ theme:

I have updated the color use for the selection background in Light theme to resolve this issue:

Test plan

See screenshot above

App preview:

• Web
• Storybook

Check out the client app preview documentation to learn more.