Update file extensions from .lua to .luau and adjust README for glob ignore tests

- Changed return statements in `init.client.lua` and `init.lua` files to reflect the new .luau extension.
- Updated README in `ignore_glob_spec` to specify that glob ignores now work with .spec.luau files instead of .spec.lua.
- Modified various test files to transition from .json to .json5 format, ensuring consistency across project configurations.

src/cli/sourcemap.rs

@@ -50,7 +50,7 @@ pub struct SourcemapCommand {
     /// Where to output the sourcemap. Omit this to use stdout instead of
     /// writing to a file.
     ///
-    /// Should end in .json.
+    /// Should end in .json5.
     #[clap(long, short)]
     pub output: Option<PathBuf>,