Best way to Add FastExpressionCompiler LightExpression

[MattEdwardsWaggleBee]

We want to add support for FastExpressionCompiler LightExpression, but should figure out the cleanest way.

Ideas:

• Add FEC Light and use options for how the expressions are built
• Define a new Compiler constant (e.g. #define FEC_LIGHT_EXPRESSION and produce two Nugets
• Other ideas?