v2024.0304.184309

Fix `import_dirs` support (#114)

`import_dirs` arguments come through as part of the `ctx.files` list and
need to have their `path` extracted when building the `embossc`
command-line. This CL also adds a `testdata` entry that checks that
`emboss_cc_library` works when specifying `import_dirs`.

Test: bazel build '//testdata:import_dir_importer_emboss'