The nested Swift module structure is recommended for Swift projects.
This structure has an outer directory called
`<Swift_MODULE_NAME>.swiftmodule` that contains generated files for the
interface. The binary swift modules, textual swift interface, and other
supplemental outputs that make up the interface to a Swift library all
go in this outer directory with the Swift module triple as the filename
followed by the appropriate file extension based on what that file
contains.
Issue: #19284
Swift compile commands need to have all source files in the module
specified in the compile command or LSP systems will report errors on
missing types that are defined in other source files in the same module.
Issue: #25491
