fix(useElementSize): add as prop for component usage

[menghany]

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.

⚠️ Slowing down new functions

Warning: Slowing down new functions

As the VueUse audience continues to grow, we have been inundated with an overwhelming number of feature requests and pull requests. As a result, maintaining the project has become increasingly challenging and has stretched our capacity to its limits. As such, in the near future, we may need to slow down our acceptance of new features and prioritize the stability and quality of existing functions. Please note that new features for VueUse may not be accepted at this time. If you have any new ideas, we suggest that you first incorporate them into your own codebase, iterate on them to suit your needs, and assess their generalizability. If you strongly believe that your ideas are beneficial to the community, you may submit a pull request along with your use cases, and we would be happy to review and discuss them. Thank you for your understanding.

---

Description

UseElementSize component as prop is ignore

Additional context

---

🤖 Generated by Copilot at 0494fc5

Added the as prop to the UseElementSize component and other components that use the useResizeObserver hook. This prop lets the user customize the root element of the component for better semantics or accessibility.

🤖 Generated by Copilot at 0494fc5

• Add as prop to UseElementSize, UseElementBounding, UseMouse, and UseMouseInElement components to allow customizing the root element tag or component (link, )