Rename "Prompt Library" to "Rules Library" (#29349)

There's probably more to do to fully make the transition, and we'll
still debate a bit internally whether this is the name, but just opening
this PR up now for visibility.

Release Notes:

- N/A

Cargo.toml

@@ -109,7 +109,7 @@ members = [
     "crates/project",
     "crates/project_panel",
     "crates/project_symbols",
-    "crates/prompt_library",
+    "crates/rules_library",
     "crates/prompt_store",
     "crates/proto",
     "crates/recent_projects",
@@ -319,7 +319,7 @@ prettier = { path = "crates/prettier" }
 project = { path = "crates/project" }
 project_panel = { path = "crates/project_panel" }
 project_symbols = { path = "crates/project_symbols" }
-prompt_library = { path = "crates/prompt_library" }
+rules_library = { path = "crates/rules_library" }
 prompt_store = { path = "crates/prompt_store" }
 proto = { path = "crates/proto" }
 recent_projects = { path = "crates/recent_projects" }