Fix OpenCL keyword identifier escaping

[alexgduarte]

Fixes #54

Summary

• mangle Java identifiers that collide with OpenCL reserved words before emitting OpenCL
• apply the same escaping to fields, locals, method parameters, and generated array helper names
• add a regression test covering field, parameter, and local identifiers named after OpenCL keywords

Testing

• Compiled main sources with javac 25 using -source 8 -target 8 against Maven-fetched dependencies
• Ran org.junit.runner.JUnitCore com.aparapi.codegen.test.OpenCLKeywordIdentifierTest
• Ran org.junit.runner.JUnitCore com.aparapi.codegen.test.PostIncLocalTest