fix(js_semantic_model): handle bogus conditional type

[Conaclos]

Summary

Fix #1695

Our semantic model defers the binding of infer T once the scope of the true branch of a conditional type is defined.
However, we miss an edge case: when the true branch is absent, infer T is never bound.
This leads to the error observed in #1695, where noUnusedVariables tries to obtain the undefined binding of infer T.
To solve the issue I added a fallback: if the true branch is absent, we bind the infer declarations in the scope of the conditional type.

Test Plan

I added a non-regression test.

[github-actions]

Parser conformance results on

js/262

Test result	main count	This PR count	Difference
Total	49701	49701	0
Passed	48721	48721	0
Failed	980	980	0
Panics	0	0	0
Coverage	98.03%	98.03%	0.00%

jsx/babel

Test result	main count	This PR count	Difference
Total	40	40	0
Passed	37	37	0
Failed	3	3	0
Panics	0	0	0
Coverage	92.50%	92.50%	0.00%

symbols/microsoft

Test result	main count	This PR count	Difference
Total	6322	6322	0
Passed	2036	2036	0
Failed	4286	4286	0
Panics	0	0	0
Coverage	32.20%	32.20%	0.00%

ts/babel

Test result	main count	This PR count	Difference
Total	662	662	0
Passed	593	593	0
Failed	69	69	0
Panics	0	0	0
Coverage	89.58%	89.58%	0.00%

ts/microsoft

Test result	main count	This PR count	Difference
Total	17646	17646	0
Passed	13439	13439	0
Failed	4205	4205	0
Panics	2	2	0
Coverage	76.16%	76.16%	0.00%