[docs][runtime] Update docs and add csyn support to Vitis HLS

[chhzh123]

Description

As the title mentions, now we can use s.build(target="vitis_hls", mode="csyn") to only invoke HLS.

Checklist

• PR's title starts with a category (e.g. [Bugfix], [IR], [Builder], etc)
• Changes are complete (i.e. I finished coding on this PR)
• All changes have test coverage (It would be better to provide ~2 different test cases to test the robustness of your code)
• Code is well-documented