Support for editing BasicBlock in every block

[shivaji17]

Is it possible to add support for returning pointer to BasicBlock which is part of every block type? This would help editing the basic block field without needing to type cast Block interface to concrete block type object.
Something similar to this

type Block interface {
	...
        ...
        ...
	GetBasicBlock() *BasicBlock.  <-  New addition
}
...
...
...
func (b *BasicBlock) GetBasicBlock() *BasicBlock {
	return b
}

If any client wants to edit something from BasicBlock which is common to all blocks, the client would always need to type cast the block interface to a particular block type and edit the BasicBlock info even when the client is not making any change specific to given block type.

[shivaji17]

@jomei Can we add support for above thing?