refactor: get_search_paths() for vyper cli (#3778)

this is for external consumers of the compiler library, which may want
to be able to replicate how vyper computes the search path

vyper/cli/vyper_compile.py

@@ -229,32 +229,37 @@ def exc_handler(contract_path: ContractPath, exception: Exception) -> None:
     raise exception
 
 
-def compile_files(
-    input_files: list[str],
-    output_formats: OutputFormats,
-    paths: list[str] = None,
-    show_gas_estimates: bool = False,
-    settings: Optional[Settings] = None,
-    storage_layout_paths: list[str] = None,
-    no_bytecode_metadata: bool = False,
-) -> dict:
-    # lowest precedence search path is always sys path
-    search_paths = [Path(p) for p in sys.path]
+def get_search_paths(paths: list[str] = None) -> list[Path]:
+    # given `paths` input, get the full search path, including
+    # the system search path.
+    paths = paths or []
 
-    # python sys path uses opposite resolution order from us
+    # lowest precedence search path is always sys path
+    # note python sys path uses opposite resolution order from us
     # (first in list is highest precedence; we give highest precedence
     # to the last in the list)
-    search_paths.reverse()
+    search_paths = [Path(p) for p in reversed(sys.path)]
 
     if Path(".") not in search_paths:
         search_paths.append(Path("."))
 
-    paths = paths or []
-
     for p in paths:
         path = Path(p).resolve(strict=True)
         search_paths.append(path)
 
+    return search_paths
+
+
+def compile_files(
+    input_files: list[str],
+    output_formats: OutputFormats,
+    paths: list[str] = None,
+    show_gas_estimates: bool = False,
+    settings: Optional[Settings] = None,
+    storage_layout_paths: list[str] = None,
+    no_bytecode_metadata: bool = False,
+) -> dict:
+    search_paths = get_search_paths(paths)
     input_bundle = FilesystemInputBundle(search_paths)
 
     show_version = False