simplify Barriers to the Identity if only_visual=True

[albi3ro]

In our compilation functions, only Barriers where only_visual=False affect the output of the compilation. If only_visual=True, the Barriers are removed prior to compilation.

We should mimic this behaviour with the qml.simplify pipeline. With this PR and #2982 , we get:

>>> qml.simplify( qml.S(0) @ qml.Barrier(0, only_visual=True) @ qml.S(0) )
PauliX(wires=[0])
>>> qml.simplify( qml.S(0) @ qml.Barrier(0, only_visual=False) @ qml.S(0) )
S(wires=[0]) @ Barrier(wires=[0]) @ S(wires=[0])

[codecov]

Codecov Report

Merging #3016 (08f7d94) into master (8978a02) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #3016   +/-   ##
=======================================
  Coverage   99.65%   99.65%           
=======================================
  Files         269      269           
  Lines       22551    22557    +6     
=======================================
+ Hits        22474    22480    +6     
  Misses         77       77           

Impacted Files	Coverage Δ
pennylane/ops/qubit/non_parametric_ops.py	100.00% <100.00%> (ø)

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

[AlbertMitjans]

Nice!