Discover workspaces without using them in resolution (#3585)

Add minimal support for workspace discovery, only used for determining
paths in the bluejay commands.

We can now discover the workspace structure, namely that the
`pyproject.toml` of a package belongs to a workspace `pyproject.toml`
with members and exclusion. The globbing logic is inspired by cargo. We
don't resolve `workspace = true` metadata declarations yet.

scripts/workspaces/albatross-in-example/src/albatross/__init__.py

@@ -0,0 +1,9 @@
+import tqdm
+
+
+def fly():
+    pass
+
+
+if __name__ == '__main__':
+    print("Caw")