[ty] Add naive implementation of completions for unimported symbols

This re-works the `all_symbols` based added previously to work across
all modules available, and not just what is directly in the workspace.

Note that we always pass an empty string as a query, which makes the
results always empty. We'll fix this in a subsequent commit.

crates/ty_python_semantic/src/module_resolver/list.rs

@@ -12,6 +12,20 @@ use super::resolver::{
     ModuleResolveMode, ResolverContext, is_non_shadowable, resolve_file_module, search_paths,
 };
 
+/// List all available modules, including all sub-modules, sorted in lexicographic order.
+pub fn all_modules(db: &dyn Db) -> Vec<Module<'_>> {
+    let mut modules = list_modules(db);
+    let mut stack = modules.clone();
+    while let Some(module) = stack.pop() {
+        for &submodule in module.all_submodules(db) {
+            modules.push(submodule);
+            stack.push(submodule);
+        }
+    }
+    modules.sort_by_key(|module| module.name(db));
+    modules
+}
+
 /// List all available top-level modules.
 #[salsa::tracked]
 pub fn list_modules(db: &dyn Db) -> Vec<Module<'_>> {

crates/ty_python_semantic/src/module_resolver/mod.rs

@@ -1,6 +1,6 @@
 use std::iter::FusedIterator;
 
-pub use list::list_modules;
+pub use list::{all_modules, list_modules};
 pub(crate) use module::KnownModule;
 pub use module::Module;
 pub use path::{SearchPath, SearchPathValidationError};