[0.0.111-bindings] Add a bindings-only version of Future::register_callback

[TheBlueMatt]

While we could, in theory, add support to the bindings logic to map
Box<dyn Trait>, there isn't a whole lot of use doing so when its
incredibly trivial to do directly.

This adds a trivial wrapper around Future::register_callback that
is only built in bindings and which is linked in the
register_callback docs for visibility.

This also has a backport of #1734 because why not.

[TheBlueMatt]

Oops, right, this should go upstream first. Please bikeshed the function name at #1737 instead and we should land that first.

[codecov-commenter]

Codecov Report

Base: 90.75% // Head: 90.78% // Increases project coverage by +0.03% 🎉

Coverage data is based on head (e498e22) compared to base (b4a40f6).
Patch has no changes to coverable lines.

Additional details and impacted files

@@                 Coverage Diff                  @@
##           0.0.111-bindings    #1736      +/-   ##
====================================================
+ Coverage             90.75%   90.78%   +0.03%     
====================================================
  Files                    86       86              
  Lines                 46530    46530              
  Branches              46530    46530              
====================================================
+ Hits                  42227    42242      +15     
+ Misses                 4303     4288      -15     

Impacted Files	Coverage Δ
lightning/src/routing/scoring.rs	96.14% <ø> (ø)
lightning/src/util/wakers.rs	86.70% <ø> (ø)
lightning/src/ln/payment_tests.rs	98.82% <0.00%> (+0.13%)	⬆️
lightning/src/ln/functional_tests.rs	96.98% <0.00%> (+0.19%)	⬆️
lightning-net-tokio/src/lib.rs	77.03% <0.00%> (+0.30%)	⬆️

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[dunxen]

Is the rename from #1734, not a breaking change? Or are we okay with that?

[TheBlueMatt]

Yea, it's not breaking, but we also backported the adoption of the struct itself, and it seems more annoyance than it's worth to ship a struct and then rename it in the next release.