ImageVisualShaderFactory refactoring

ImageVisualShaderFactory refactoring

 ImageVisualShaderFactory::GetShader method is too long and complex.
 The method uses same logic for two different purpose in a method
 that makes difficult to understand.
 And the method also has too many braces depth.

 This patch moves some features that to create shaderType and
 to retrive shaderPreFix to ImageVisualShaderFeatureBuilder.
 Now ImageVisualShaderFeatureBuilder manages all responsibility
 to define shader codes following its options.
 And slides some codes for readability and it make possible remove
 unnecessary comments.

Change-Id: I09a725d4e101cb65badffe3a897572971e2c336b
Signed-off-by: seungho baek <sbsh.baek@samsung.com>