Try and be a bit nicer about handling bad [feature] definitions (#9606)

* Try and be a bit nicer about handling bad [feature] definitions - they're single square bracket defined and require strings for feature bound values.

* Some more tweaks to the feature system to output useful and well formatted error messages when bounds fail. Requires SPI 7.0.1 and the language string "fml.modloading.feature.missing" has changed.

* Use immutable lists where possible and generally tidy things a bit

src/main/resources/META-INF/mods.toml

@@ -62,3 +62,9 @@ description='''${mod_description}'''
     versionRange="${minecraft_version_range}"
     ordering="NONE"
     side="BOTH"
+
+# Features are specific properties of the game environment, that you may want to declare you require. This example declares
+# that your mod requires GL version 3.2 or higher. Other features will be added. They are side aware so declaring this won't
+# stop your mod loading on the server for example.
+#[features.${mod_id}]
+#openGLVersion="[3.2,)"