[Analysis API] Collect designations only for autonomous declarations

Parameters, type parameters, and property accessors are not
self-sufficient declarations (their resolution depends on resolution
of their parent), so a proper designation path cannot be computed
for them.

Without a designation path, 'ContextCollector' performs analysis of the
whole file, which is inefficient.

analysis/low-level-api-fir/testData/contextCollector/propertyAccessor.kt

@@ -0,0 +1,4 @@
+class Foo {
+    val x: Int
+        <expr>get() = 42</expr>
+}