Consider open unattached scriptInfo for external files

[znck]

This prevents unnecessary inferred project creation and .vue files
referenced in .ts/.js rootFiles are included in correct project.

[codecov-commenter]

Codecov Report

Merging #303 (785d383) into main (9c20060) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

❗ Current head 785d383 differs from pull request most recent head eee6e00. Consider uploading reports for the commit eee6e00 to get more accurate results

@@            Coverage Diff             @@
##             main     #303      +/-   ##
==========================================
- Coverage   35.22%   35.20%   -0.02%     
==========================================
  Files         164      164              
  Lines       20878    20883       +5     
  Branches      840      840              
==========================================
- Hits         7354     7352       -2     
- Misses      13524    13531       +7     

Impacted Files	Coverage Δ
...plugin-vue/src/services/TypescriptPluginService.ts	0.00% <0.00%> (ø)
packages/shared/src/rpc/handlers.ts	97.42% <0.00%> (-0.52%)	⬇️

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