Implement icall used by RuntimeHelpers.EnsureSufficientExecutionStack…

… on netcore Mono.

Current implementation always returned true for Windows/Linux/Android.
There are however use of this API in Task library to make sure recursive
tasks won't hit stackoverflow. There are several tests in System.Threading.Tasks
that currently hit this, at least on Windows, causing test failures.

Fix use stack limits already setup in register_thread and used by GC when
doing conservative stack scan. If the limits have not been setup or is not
supported on platform, we will use old defaults, always assume there is
enough stack space available. Heuristics around size of minimum execution
stack needed are picked from corresponding CoreCLR implementation.

src/mono/mono/metadata/icall.c

@@ -126,6 +126,16 @@
 
 //#define MONO_DEBUG_ICALLARRAY
 
+// Inline with CoreCLR heuristics, https://github.com/dotnet/runtime/blob/385b4d4296f9c5cb82363565aa210a1a37f92d90/src/coreclr/src/vm/threads.cpp#L6344.
+// Minimum stack size should be sufficient to allow a typical non-recursive call chain to execute,
+// including potential exception handling and garbage collection. Used for probing for available
+// stack space through RuntimeHelpers.EnsureSufficientExecutionStack.
+#if TARGET_SIZEOF_VOID_P == 8
+#define MONO_MIN_EXECUTION_STACK_SIZE (128 * 1024)
+#else
+#define MONO_MIN_EXECUTION_STACK_SIZE (64 * 1024)
+#endif
+
 #ifdef MONO_DEBUG_ICALLARRAY
 
 static char debug_icallarray; // 0:uninitialized 1:true 2:false
@@ -1293,6 +1303,27 @@ ves_icall_System_Runtime_CompilerServices_RuntimeHelpers_RunModuleConstructor (M
 	mono_runtime_class_init_full (vtable, error);
 }
 
+#ifdef ENABLE_NETCORE
+MonoBoolean
+ves_icall_System_Runtime_CompilerServices_RuntimeHelpers_SufficientExecutionStack (void)
+{
+	MonoThreadInfo *thread = mono_thread_info_current ();
+	void *current = &thread;
+
+	// Stack upper/lower bound should have been calculated and set as part of register_thread.
+	// If not, we are optimistic and assume there is enough room.
+	if (!thread->stack_start_limit || !thread->stack_end)
+		return TRUE;
+
+	// Stack start limit is stack lower bound. Make sure there is enough room left.
+	void *limit = ((uint8_t *)thread->stack_start_limit) + MONO_MIN_EXECUTION_STACK_SIZE;
+
+	if (current < limit)
+		return FALSE;
+
+	return TRUE;
+}
+#else
 MonoBoolean
 ves_icall_System_Runtime_CompilerServices_RuntimeHelpers_SufficientExecutionStack (void)
 {
@@ -1331,6 +1362,7 @@ ves_icall_System_Runtime_CompilerServices_RuntimeHelpers_SufficientExecutionStac
 #endif
 	return TRUE;
 }
+#endif
 
 #ifdef ENABLE_NETCORE
 MonoObjectHandle