Better error message when no path can be found in Graph decomposition

[rniczh]

When the graph solver cannot find a path to the requested gate_set, the underlying MLIR pass throws an uncaught C++ exception. When this happens, you may see many lines on the screen before you reach the error message below.

[libc++abi: terminating due to uncaught exception of type
  DecompGraph::Core::GraphSolverFailedError: Decomposition rule not found for operator](libc++abi: terminating due to uncaught exception of type DecompGraph::Core::GraphSolverFailedError: Decomposition rule not found for operator 'Toffoli[w:3][p:0]')

Reproduce:

import pennylane as qp
from catalyst import qjit
from catalyst.passes import graph_decomposition

@qjit(capture=True)
@graph_decomposition(gate_set={qp.RX})
@qp.qnode(qp.device("lightning.qubit", wires=3))
def t(): 
    qp.Toffoli([0,1,2])
    return qp.state()

print(t())

[rniczh]

I think we should probably use mlir::Diagnostic? I think we're not using it at all, just searched the repo, only the stablehlo contains this.