Static resources in src/main/webapp are not correctly resolved by GSP editor

The <g:resource> in IntelliJ Idea GSP editor does not correctly resolve the static resources located in src/main/webapp while at runtime Grails 3 correctly load these resources.
The editor shows a red line at the <g:resource> line and shows a balloon with the message:

Cannot resolve directory '...'
Cannot resolve file '...'

To reproduce the issue open the views/test/index.gsp in the attached example application.

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*Imported from [IDEA-166414](https://youtrack.jetbrains.com/issue/IDEA-166414) · Type: Bug · Votes: 0*
*Comments, attachments, dates and reporter are not part of the export — follow the link above for the full history.*

Open views/test/index.gsp in the attached example application and reproduce the IntelliJ GSP editor errors for the g:resource references. Compare the editor's resolution of resources under src/main/webapp with the runtime behavior; done when those static resources resolve without red-line or cannot-resolve-directory/file errors.

Written by the indexing model from the issue text.