Go to definition / open link for file path in `include_str` should work for non-Rust files

Split off from #11019. See https://github.com/rust-analyzer/rust-analyzer/issues/11019#issuecomment-994966731.

Go to definition / open link for file paths in include, include_str, include_bytes does work already (https://github.com/rust-analyzer/rust-analyzer/issues/11019#issuecomment-994479218).

Sadly, this only works if the file extension is rs. My codebase on the other hand include_strs JS and CSS files and include_bytes WOFF files (just like librustdoc!). In such a case, this feature does not work.

I would say more often than not one doesn't include_str Rust files (contrary to include). I am not sure if that still counts as jump to definition in the LSP sense but it's reasonable to support (as open link or whatever other mechanism available) in my opinion. I am not familiar with the LSP though.

rust-analyzer version: rust-analyzer version: db2a7087b 2021-12-13 stable

rustc version: rustc 1.59.0-nightly (48a5999fc 2021-12-01)

Start with the existing include/include_str/include_bytes handling discussed in #11019 and its linked comments. Reproduce the current behavior with non-Rust paths such as JS, CSS, and WOFF files; done means go-to-definition or open-link navigation works for those paths as it already does for Rust files.