[Bugfix] Interface name variations dispatch to correct backprop device

[albi3ro]

Fixes #2546

Now if you specify QNodes like:

qml.QNode(qfunc, qml.device('default.qubit', wires=1), interface="tensorflow", diff_method="backprop")

It will map the device to default.qubit.tf and using backpropagation instead of silently switching to a different diff_method.

In solving this bug, I substituted qml.interfaces.INTERFACE_MAP for qml.interfaces.INTERFACE_NAMES, which maps in the opposite direction. This allowed from some readability improvements. qml.interfaces.INTERFACE_MAP maps provided name to canonical name, instead of canonical name to list of acceptable provided names.

[albi3ro]

[sc-19268]

[codecov]

Codecov Report

Merging #2591 (ff59961) into master (48636c5) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #2591   +/-   ##
=======================================
  Coverage   99.58%   99.58%           
=======================================
  Files         243      243           
  Lines       19595    19596    +1     
=======================================
+ Hits        19514    19515    +1     
  Misses         81       81           

Impacted Files	Coverage Δ
pennylane/interfaces/__init__.py	100.00% <100.00%> (ø)
pennylane/interfaces/execution.py	100.00% <100.00%> (ø)
pennylane/qnode.py	100.00% <100.00%> (ø)

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[antalszava]

Looks good! 🎉 😻 Once the changelog entry is updated, good to merge this from my side.