Starlark: annotate builtin functions with trustReturnsValid

Speed up is 4% for this test:

```
def test():
  for i in range(10):
    print(i)
    d = {"a": range(10), "b": {}, "c": 4, "d": 5, "e": (), "f": True, "g": []}
    for _ in range(1000000):
      d.get("a")
      d.get("b")
      d.get("c")
      d.get("d")
      d.get("e")
      d.get("f")
      d.get("g")

test()
```

src/main/java/net/starlark/java/eval/Dict.java

@@ -214,6 +214,7 @@ public Iterator<K> iterator() {
             named = true,
             doc = "The default value to use (instead of None) if the key is not found.")
       },
+      trustReturnsValid = true,
       useStarlarkThread = true)
   // TODO(adonovan): This method is named get2 as a temporary workaround for a bug in
   // StarlarkAnnotations.getStarlarkMethod. The two 'get' methods cause it to get
@@ -247,6 +248,7 @@ public Object get2(Object key, Object defaultValue, StarlarkThread thread) throw
             named = true,
             doc = "a default value if the key is absent."),
       },
+      trustReturnsValid = true,
       useStarlarkThread = true)
   public Object pop(Object key, Object defaultValue, StarlarkThread thread) throws EvalException {
     Starlark.checkMutable(this);
@@ -298,7 +300,8 @@ public Tuple popitem() throws EvalException {
             defaultValue = "None",
             named = true,
             doc = "a default value if the key is absent."),
-      })
+      },
+      trustReturnsValid = true)
   public V setdefault(K key, V defaultValue) throws EvalException {
     Starlark.checkMutable(this);
     Starlark.checkHashable(key);

src/main/java/net/starlark/java/eval/MethodLibrary.java

@@ -40,7 +40,8 @@ class MethodLibrary {
               + "or if no arguments are given. "
               + "<pre class=\"language-python\">min(2, 5, 4) == 2\n"
               + "min([5, 6, 3]) == 3</pre>",
-      extraPositionals = @Param(name = "args", doc = "The elements to be checked."))
+      extraPositionals = @Param(name = "args", doc = "The elements to be checked."),
+      trustReturnsValid = true)
   public Object min(Sequence<?> args) throws EvalException {
     return findExtreme(args, Starlark.ORDERING.reverse());
   }
@@ -54,7 +55,8 @@ public Object min(Sequence<?> args) throws EvalException {
               + "or if no arguments are given. "
               + "<pre class=\"language-python\">max(2, 5, 4) == 5\n"
               + "max([5, 6, 3]) == 6</pre>",
-      extraPositionals = @Param(name = "args", doc = "The elements to be checked."))
+      extraPositionals = @Param(name = "args", doc = "The elements to be checked."),
+      trustReturnsValid = true)
   public Object max(Sequence<?> args) throws EvalException {
     return findExtreme(args, Starlark.ORDERING);
   }
@@ -625,6 +627,7 @@ public boolean hasattr(Object obj, String name, StarlarkThread thread) throws Ev
                 "The default value to return in case the struct "
                     + "doesn't have an attribute of the given name.")
       },
+      trustReturnsValid = true,
       useStarlarkThread = true)
   public Object getattr(Object obj, String name, Object defaultValue, StarlarkThread thread)
       throws EvalException, InterruptedException {

src/main/java/net/starlark/java/eval/StarlarkList.java

@@ -538,7 +538,8 @@ public int index(Object x, Object start, Object end) throws EvalException {
             },
             defaultValue = "-1",
             doc = "The index of the item.")
-      })
+      },
+      trustReturnsValid = true)
   public Object pop(Object i) throws EvalException {
     int arg = i == Starlark.NONE ? -1 : Starlark.toInt(i, "i");
     int index = EvalUtils.getSequenceIndex(arg, size);