feat: Add bashIde.shfmt.additionalArguments LSP setting.

[kylechui]

This will allow a user to extend the arguments being passed to the shfmt binary, and resolve #1385.

NOTE: I think that some of the tests had their number of arguments increased by one, since my wrapper makeShfmtConfig will impute languageDialect: 'auto' when it used to be omitted.

[kylechui]

The tests are largely passing my local machine, except for a few that rely on the get-options.sh script. I think this is because I am running NixOS, which doesn't store those completion files in the Linux FHS. I imagine if the CI for this project has tests that spin up the language server in a virtual machine, then they should pass.