Accept template arguments as a string of fully qualified type names

[FramePerfection]

This allows the following code to generate implementations for System.Single and System.Double by transforming the string constant NUMERIC_TYPES to their best matching INamedTypeSymbols based on the generator's semantic model.

const string NUMERIC_TYPES = "System.Single System.Double";

[ChaosGenerators.TemplateGenerator("=> a > b ? a : b;", NUMERIC_TYPES)]
internal delegate T _Max<T>(T a, T b);

[ChaosGenerators.TemplateGenerator("=> a < b ? a : b;", NUMERIC_TYPES)]
internal delegate T _Min<T>(T a, T b);

This eliminates the need to write out the set of types in each template delegate that expects the same "class" (in a mathematical sense) of objects, such as the numerics in this example.

The implementation is somewhat dirty, creating an exclusive relationship between the fullyQualifiedTypeNames and types fields in TemplateGeneratorAttribute, as well as the rather speculative implementation of the attribute argument evaluation in the TemplateGenerator.

[FramePerfection]

This is more of a proof of concept than a serious attempt to implement this, but since the target branch is still a draft pull-request itself, might it be okay to merge this anyways? It's missing documentation, but that should probably happen on the "main" pull-request anyways, given that the exact interface hasn't even been fully shaped yet.