[mlir] Introduce callback-based builders for AffineForOp

Similarly to `scf::ForOp`, introduce additional `function_ref` arguments to
`AffineForOp::build` that can be used to populate the body of the loop during
its construction. Provide compatibility functions for constructing affine loop
nests using `edsc::ScopedContext`.

`edsc::AffineLoopNestBuilder` and reletad functionality is now deprecated and
will be removed soon, users are expected to switch to `affineLoopNestBuilder`
that provides similar functionality with a simpler OpBuilder-based
implementation.

Differential Revision: https://reviews.llvm.org/D81754