Ship JetBrains default theme

[udaychandra]

Summary

• Bundle JetBrains light and dark themes as first-party Chorus themes
• Bundle JetBrains New UI light and dark icon themes and load bundled icon theme assets at startup
• Make JetBrains Light/Dark and JetBrains New UI Icons the default system-aware theme settings

Validation

• cargo fmt --check
• cargo check -p theme_settings -p ui -p assets
• cargo test -p theme_settings
• cargo check -p zed
• git diff --check

Release Notes:

• Added JetBrains-inspired default themes and JetBrains New UI file icons to Chorus