analyzer: mock SDK: correct declarations in math library

* `min` and `max` are external.
* Random is an `abstract interface` class (and it's members can be
  abstract).

Change-Id: I5e1e6f0d3c89aecfb1c83b09a96f0910511f8d5b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/451540
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Samuel Rawlins <srawlins@google.com>

Author: srawlins

pkg/analyzer/lib/src/test_utilities/mock_sdk.dart

@@ -1535,18 +1535,19 @@ const double e = 2.718281828459045;
 const double pi = 3.1415926535897932;
 const double ln10 = 2.302585092994046;
 
-T min<T extends num>(T a, T b) => throw 0;
-T max<T extends num>(T a, T b) => throw 0;
+external T min<T extends num>(T a, T b);
+external T max<T extends num>(T a, T b);
 
 external double cos(num radians);
 external double sin(num radians);
-external double sqrt(num radians);
+external double sqrt(num x);
 external double tan(num radians);
 
-class Random {
-  bool nextBool() => true;
-  double nextDouble() => 2.0;
-  int nextInt() => 1;
+abstract interface class Random {
+  external factory Random([int? seed]);
+  bool nextBool();
+  double nextDouble();
+  int nextInt(int max);
 }
 
 class Point<T extends num> {}

pkg/analyzer/test/src/dart/analysis/search_test.dart

@@ -992,6 +992,8 @@ Random v2;
   20 2:1 |Random| REFERENCE
 <testLibraryFragment> v2@38
   31 3:1 |Random| REFERENCE
+dart:math new@null
+  402 16:20 |Random| REFERENCE
 ''');
   }