Region decomp hierarchical groupping + Visualization

[hon-gyu]

Example

    let classify (x : int) (y : int) : int =
    if x > 0 then
        if y > 0 then
        if x > y then 1
        else 2
        else
        if y < -10 then 3
        else 4
    else
        if y > 0 then 5
        else 6"""

├── [1] constraint='x <= 0' invariant=None (w=2, n_children=2, n_descendants=2)
│   ├── [1.1] constraint='y <= 0' invariant='6' (w=1, n_children=0, n_descendants=0)
│   └── [1.1.2] constraint='y >= 1' invariant='5' (w=1, n_children=0, n_descendants=0)
├── [1.2.1.1] constraint='y >= (-10)' invariant='4' (w=1, n_children=0, n_descendants=0)
├── [1.2.3] constraint='y >= 1' invariant=None (w=2, n_children=2, n_descendants=2)
│   ├── [1.2.3.1.1] constraint='x >= 1' invariant='2' (w=1, n_children=0, n_descendants=0)
│   └── [1.2.3.1.2.1] constraint='not (x <= y)' invariant='1' (w=1, n_children=0, n_descendants=0)
└── [1.2.3.4.1] constraint='y <= (-11)' invariant='3' (w=1, n_children=0, n_descendants=0)\

See added tests for details