Problem:    Typst filetype is not recognized.
Solution:   Distinguish between sql and typst. (Gaetan Lepage, closes #12363)

Problem:    Global 'filetype' is set when it is detected from the file content.
Solution:   Set the local 'filetype' option value.

Problem:    Filetypes for *.v files not detected properly.
Solution:   Use the file contents to detect the filetype. (Turiiya,
            closes #12281)

Problem:    Strace filetype detection is expensive.
Solution:   Match with a cheap pattern first. (Federico Mengozzi,
            closes #12220)

Problem:    .fs files are falsely recognized as forth files.
Solution:   Check 100 lines for something that looks like forth. (Johan
            Kotlinski, closes #12219, closes #11988)