feat(useAbs): new function

[LittleSound]

From #1812

Description

Reactively Math.abs(value).

Usage

import { useAbs } from '@vueuse/math'

const value = ref(-23)
const absValue = useAbs(value)

// absValue.value: 23

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Before submitting the PR, please make sure you do the following

• 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.