gradle: add properties and modify injected-client (#1145)

* add implementation for getItemCount

* Ignore build directory in project root

* save injector results as class files

* package injected-client for shading into client

* auto-updating properties

* fix run task

* shade injected-client into jar

runescape-api/src/main/java/net/runelite/rs/api/RSClient.java

@@ -1045,4 +1045,7 @@ public interface RSClient extends RSGameShell, Client
 	BigInteger getModulus();
 
 	void setModulus(BigInteger modulus);
+
+	@Import("ItemDefinition_fileCount")
+	int getItemCount();
 }