[lldb][test] Remove symlink for API tests.

Summary: Moves lldbsuite tests to lldb/test/API.

This is a largely mechanical change, moved with the following steps:

```
rm lldb/test/API/testcases
mkdir -p lldb/test/API/{test_runner/test,tools/lldb-{server,vscode}}
mv lldb/packages/Python/lldbsuite/test/test_runner/test lldb/test/API/test_runner
for d in $(find lldb/packages/Python/lldbsuite/test/* -maxdepth 0 -type d | egrep -v "make|plugins|test_runner|tools"); do mv $d lldb/test/API; done
for d in $(find lldb/packages/Python/lldbsuite/test/tools/lldb-vscode -maxdepth 1 -mindepth 1 | grep -v ".py"); do mv $d lldb/test/API/tools/lldb-vscode; done
for d in $(find lldb/packages/Python/lldbsuite/test/tools/lldb-server -maxdepth 1 -mindepth 1 | egrep -v "gdbremote_testcase.py|lldbgdbserverutils.py|socket_packet_pump.py"); do mv $d lldb/test/API/tools/lldb-server; done
```

lldb/packages/Python/lldbsuite/__init__.py and lldb/test/API/lit.cfg.py were also updated with the new directory structure.

Reviewers: labath, JDevlieghere

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D71151

lldb/test/API/python_api/thread/main2.cpp

@@ -0,0 +1,53 @@
+//===-- main.c --------------------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+#include <stdio.h>
+#include <stdlib.h>
+
+int a(int);
+int b(int);
+int c(int);
+
+int a(int val)
+{
+    if (val <= 1)
+        return b(val);
+    else if (val >= 3)
+        return c(val);
+
+    return val;
+}
+
+int b(int val)
+{
+    int rc = c(val);
+    void *ptr = malloc(1024); // thread step-out of malloc into function b.
+    if (!ptr)
+        return -1;
+    else
+        printf("ptr=%p\n", ptr);
+    return rc;                // we should reach here after 3 step-over's.
+}
+
+int c(int val)
+{
+    return val + 3;
+}
+
+int main (int argc, char const *argv[])
+{
+    int A1 = a(1);
+    printf("a(1) returns %d\n", A1);
+    
+    int B2 = b(2);
+    printf("b(2) returns %d\n", B2);
+    
+    int A3 = a(3);
+    printf("a(3) returns %d\n", A3);
+    
+    return 0;
+}