feat(useClamp): composable computed usage improvements

[clemdee]

Description

This PR aims to improve computed usage of the useClamp composable:

• feat: make composable accept a function as value parameter
• fix: when passing a computed value, the composable was throwing as "Write operation failed: computed value is readonly" warning, because it was trying to set the value of its internal ref, which was a computed ref in that case
• docs: took the opportunity to add an example about the computed usage of useClamp in the doc

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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• Read the Contributing Guidelines.
• Read the Pull Request Guidelines.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Ideally, include relevant tests that fail without this PR but pass with it.