[Build] Move sourceCompatibility option to the root build file

imgui-binding/build.gradle

@@ -1,4 +1,4 @@
-import imgui.generate.GenerateLibs
+import tool.generator.GenerateLibs
 
 plugins {
     id 'java'
@@ -7,8 +7,6 @@ plugins {
     id 'signing'
 }
 
-sourceCompatibility = 1.8
-
 dependencies {
     testImplementation 'org.junit.jupiter:junit-jupiter-api:5.5.2'
     testImplementation 'org.junit.jupiter:junit-jupiter-engine:5.5.2'