Use CairoBlockFunctionDefinition node for Cairo Blocks

[cicr99]

There is an implementation for CairoBlockFunctionDefinition nodes in src/ast/cairoNodes/cairoBlockFunctionDefinition.ts that is not being used at the moment. Cairo blocks are currently being handled using the documentation of FunctionDefinition nodes. Using an instance of the class CairoBlockFunctionDefinition to represent the block will make it easier to handle
Some places that will need updating when doing the refactor:

• src/passes/cairoStubProcessor.ts
• src/cairoWriter/writers/cairoFunctionDefinitionWriter.ts
• src/passes/annotateImplicits.ts

Refer to the documentation for further details on Cairo Blocks