Add OnServicesDiscovered event

[twyatt]

Encapsulates the service discovery response in OnServicesDiscovered event class, making it consistent with how other events are propagated.

Improves the logging of the event (in CoroutinesGatt.performBluetoothAction). Prior to this change the response was logged as:

I/Able: onServicesDiscovered ← 0

By wrapping in event class, log will now appear as:

I/Able: onServicesDiscovered ← OnServicesDiscovered(status=GATT_SUCCESS(0))

[codecov]

Codecov Report

Merging #52 into develop will increase coverage by 0.28%.
The diff coverage is 100.00%.

@@              Coverage Diff              @@
##             develop      #52      +/-   ##
=============================================
+ Coverage      76.22%   76.51%   +0.28%     
  Complexity        35       35              
=============================================
  Files             12       12              
  Lines            244      247       +3     
  Branches          26       26              
=============================================
+ Hits             186      189       +3     
  Misses            50       50              
  Partials           8        8              

Impacted Files	Coverage Δ	Complexity Δ
core/src/main/java/gatt/CoroutinesGatt.kt	50.00% <100.00%> (+1.28%)	10.00 <1.00> (ø)
core/src/main/java/gatt/Events.kt	72.85% <100.00%> (+1.21%)	0.00 <0.00> (ø)
core/src/main/java/gatt/GattCallback.kt	83.78% <100.00%> (-0.43%)	17.00 <1.00> (ø)