fix: normalize image source

[brc-dd]

fixes #450

[meteorlxy]

I'm afraid it's not an ideal fix. Two problems:

• The raw html <img> tag is not handled, then the behaviors of <img src="foo"> and ![](foo) are inconsistent.
• It makes the vite.resolve.alias fail to work, because the plugin will prepend ./ to the alias.

[meteorlxy]

IMO, the original behavior is consistent with vite + vue DX, so we might not need this plugin.