CLI glob pattern does not preserve files location

Not necessarily a bug, as #90 does not mention any particular outcome or use case scenarios. It would be helpful to extend this functionality to preserve directory structure when used with glob pattern and without --bundle, single file output.

With nested dir structure:

+ /resources/css
+-+ /components
    +-- /button.css
    +-- /input.css
+-+ /sections
    +-- /newsletter.css
    +-- /cta.css
+-- /layout.css
+-- /reset.css

CLI command with glob pattern #90:

lightningcss resources/css/**/*.css --output-dir public/css

Will produce flat output (missing subfolders) and root lvl files (layout.css and reset.css) are lost:

+ /public/css
+-- /button.css
+-- /input.css
+-- /newsletter.css
+-- /cta.css

Expected output would be to preserve the structure and root lvl files:

+ /public/css
+-+ /components
    +-- /button.css
    +-- /input.css
+-+ /sections
    +-- /newsletter.css
    +-- /cta.css
+-- /layout.css
+-- /reset.css

Current behavior creates few problems:

• file names has to be unique in different folders
• some files are lost from glob pattern
• complicates build scripts with multiple calls *
• build scripts are not dynamic as each subdir has to be added manually

*It is possible to workaround this by calling CLI multiple times (but that's not glob support mentioned in #90):

lightningcss resources/css/components/*.css --output-dir public/css/components
lightningcss resources/css/sections/*.css --output-dir public/css/sections
lightningcss resources/css/*.css --output-dir public/css

Start by locating the CLI glob expansion and --output-dir handling, then run the documented lightningcss resources/css/**/*.css --output-dir public/css command against the nested example. Done means matching subdirectories are preserved, root-level files are included, and the resulting public/css tree matches the expected structure.