Turbine: fast-path simple class types and empty type parameters in TypeBinder.

TypeBinder previously flattened every Tree.ClassTy via t.flatten() and bindClassTyRest (allocating two ImmutableLists even for unqualified simple type names), and unconditionally appended empty MapScope wrappers to CompoundScope and invoked bindTyParams (allocating a LinkedHashMap) for every class and method even when typarams().isEmpty().

• Fast-path single-identifier class type binding in TypeBinder.bindClassTy when t.base().isEmpty(), avoiding t.flatten() and intermediate list allocations for unqualified type names.
• Skip appending an empty MapScope to CompoundScope and calling bindTyParams in TypeBinder.bind and TypeBinder.bindMethod when typarams().isEmpty(), shortening the CompoundScope chain traversed by subsequent scope.lookup calls.
• Fast-path TypeBinder.bindAnnotations when trees.isEmpty() and pre-size the ImmutableList builder when annotations are present.

On Chromium’s chrome_java target (1,752 source files, 4,565 classes), running on the JVM (-Xms6g -Xmx6g -Xmn5g -XX:+UseParallelGC, 15 warmup + 15 measured iterations), this reduces TypeBinder phase time by 17.75 ± 3.77 ms (25.3%; 95% CI 20.0–30.7%), from 70.06 ± 3.54 ms (median 71.63 ms) to 52.31 ± 1.29 ms (median 53.18 ms). The output is byte-for-byte identical.

PiperOrigin-RevId: 1007456988