Modernize our vbuild to use ESM import rather than inlining the JS

[evnchn]

Motivation

The mastermind is and always has been @xaptronic (see #4673), but things went stale and that PR becomes harder and harder to merge as time marches onwards.

The potential advantages are at #4673 (comment) but you should read above the first --- because the rest are about the refactoring of vbuild and no AI can beat @falkoschindler (look at #5255)

Implementation

The logic is 3:

1. Cut the middleman create_vue_component between self.script and parser.script (check Allow nicegui SFC script section to use ESM / import syntax #4673 (comment))
2. Use js_imports instead of vue_scripts
3. Serve vue_components from _get_component

Progress

• I chose a meaningful title that completes the sentence: "If applied, this PR will..."
• The implementation is complete.
  • The pytest should pass, obviously
  • We really need to have our own set of pytest to test whether our Vue integration works. We already winged it in Move vbuild into our repository #5255, and we don't want to double-wing it.
• Pytests have been added (or are not necessary).
• Documentation has been added (or is not necessary).