[SR-13700] Differentiation transform: support optional-related operations

[dan-zheng]

Previous ID	SR-13700
Radar	None
Original Reporter	@dan-zheng
Type	Sub-task

Additional Detail from JIRA

Votes	0
Component/s
Labels	Sub-task
Assignee	None
Priority	Medium

md5: cf7d5719c3aab6c5415a45d1064ed7d5

Parent-Task:

• SR-13695 Enum differentiation

is blocked by:

• SR-13698 Conditionally conform Optional to Differentiable

Issue Description:

Support differentiation of Optional-related operations:

if let x = optional { ... } // if-let bindings
x! // force unwrapping
x?.foo(y) // optional chaining
x ?? y // nil coalescing
for x in array { ... } // for-in loops

Some of these may naturally work after TF-583.