Allow specifying output directory (not filename)

Description

I'd like a command line switch to set the output directory, and have the filename be the same that would normally be generated automatically (so x.typ becomes x.pdf).

Use Case

Currently I have to type the filename twice if I want to output to a different directory. This is annoying and error prone. If I'm working with multiple .typ files, I have to remember to keep changing both filenames when I'm compiling a different file. Writing a script or a Makefile to handle this for me (which I might want to do to set other options like a font directory) is more annoying than it should be, because I have to manually parse the input filename to remove the extension and add .pdf from within the script.

Start by tracing the command-line handling for output paths and the existing automatic filename generation. Add an output-directory option that preserves that generated filename, then verify that compiling one or more .typ inputs places the resulting PDFs in the requested directory without requiring a filename.