1503 - C# compiler should use CSAssembly.
Description
    
CSAssembly exposes the functionality necessary to correctly compile C# code.
ObjectList/Library should not be used to compile C# code.
    
Example
    
Config:
    Compiler( 'CSharpCompiler' )
{
    .Executable         = 'csc.exe'
}
ObjectList( 'ObjectList' )
{
    .Compiler           = 'CSharpCompiler' // Invalid
    .CompilerOptions    = '/out:"%2" /target:library "%1"'
    .CompilerInputFiles = 'src/file.cs'
    .CompilerOutput     = 'out/output.dll'
}
Output:
C:\test\fbuild.bff(6,1): FASTBuild Error #1503 - ObjectList() - C# compiler should use CSAssembly.
ObjectList( 'ObjectList' )
^
\--here
Fix:
Compiler( 'CSharpCompiler' )
{
    .Executable         = 'csc.exe'
}
CSAssembly( 'CSharp' )
{
    .Compiler           = 'CSharpCompiler'
    .CompilerOptions    = '/out:"%2" /target:library "%1"'
    .CompilerInputFiles = 'src/file.cs'
    .CompilerOutput     = 'out/output.dll'
}
    