Add lint check for expect/actual samples

Expect/actual samples will break samples resolution within dackka.

This updates how the samples lint check processes functions. Previously, it visited `UMethod`s, but that skips visiting `expect` declarations. Now it instead visits all `KtFunction`s in a file (samples functions must be in Kotlin).

This lint check is limited by the fact that lint only runs for jvm/android compilations. If a samples project doesn't have jvm or android as a target, it will miss expect/actual samples declarations (these will instead be caught by dackka failing).

Bug: 181224204
Test: SampledAnnotationDetectorTest
Change-Id: I4ff04b447240f7a7b9f81aa4f4a31954181388f3