feat(full-screen): add current time display in full screen mode

[daksh2k]

Fixes #183

Add an option to display the current time in full screen mode.

• Add showCurrentTime setting to DEFAULTS in Extensions/full-screen/src/constants/defaults.ts.
• Update the render function in Extensions/full-screen/src/app.tsx to include a time display element and update it every second.
• Add styles for the time display element in Extensions/full-screen/src/styles/base.scss.
• Add HTML to include the current time display element in Extensions/full-screen/src/services/html-creator.ts.
• Add string for showCurrentTime setting in Extensions/full-screen/src/resources/locales/en-US.json.

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