fix(cli): convert the sourcemap option to boolean (fix #13638)

[dd-jonas]

Description

Fix #13638

ee3b90a added 'inline' and 'hidden' as options to --sourcemap in the CLI and broke the behavior of booleans, i.e. true and false became strings. This resulted in --sourcemap false to still output sourcemaps.

Additional context

There's not really a clean way to convert 'true' and 'false' to a boolean. Feel free to suggest a different approach.
Also, I'm not sure if a test case should be added for this. It's my first contribution and didn't see tests related to CLI options.

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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