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

crates/rules_library/Cargo.toml

@@ -0,0 +1,34 @@
+[package]
+name = "rules_library"
+version = "0.1.0"
+edition.workspace = true
+publish.workspace = true
+license = "GPL-3.0-or-later"
+
+[lints]
+workspace = true
+
+[lib]
+path = "src/rules_library.rs"
+
+[dependencies]
+anyhow.workspace = true
+collections.workspace = true
+editor.workspace = true
+gpui.workspace = true
+language.workspace = true
+language_model.workspace = true
+log.workspace = true
+menu.workspace = true
+picker.workspace = true
+prompt_store.workspace = true
+release_channel.workspace = true
+rope.workspace = true
+serde.workspace = true
+settings.workspace = true
+theme.workspace = true
+ui.workspace = true
+util.workspace = true
+workspace-hack.workspace = true
+workspace.workspace = true
+zed_actions.workspace = true

crates/rules_library/LICENSE-GPL

@@ -0,0 +1 @@
+../../LICENSE-GPL