[DAP] Fix the missing exception breakpoints

Summary:
In D59401005, `ResetDebuggerState()` was added as a part of the "reuse lldb-dap" change. The intention of the method is to reset any state related to the debugger, so that it will be a clean start for new debug sessions.

However, clearing `exception_breakpoints` will cause exception breakpoints to disappear in VS Code for new debug sessions. See first video in "Test Plan" section.

Here is why:
The exception breakpoints are added into `exception_breakpoints` by `PopulateExceptionBreakpoints()`. This function has a `llvm::call_once` - it will only execute once during the whole lifetime of the process. Clearing `exception_breakpoints` at the end of the 1st debug session means that any 2nd+ sessions will see an empty list. See diff comment.

The following properties are true:
1. In a single debug session, the list of `ExceptionBreakpoint` objects (and the `SBBreakpoint` objects within) remain the same. This ensures consistency within the session when the list of exception breakpoints are interacted.
2. When reusing lldb-dap, the list is cleared between sessions and is repopulated the first time `PopulateExceptionBreakpoints()` is called in each session. This differs from before the diff, where 2nd+ sessions don't repopulate the list. This fixes the bug.

Test Plan:

By debugging a c++ toy program and observe the existence of the exception breakpoints in VS Code Local.

**Before the change:** Exception breakpoints exist for the 1st debug session, but disappears for 2nd+ sessions.
https://pxl.cl/6CBK7

**After the change:** Exception breakpoints exist for all debug sessions.
https://pxl.cl/6CBKl

**Test fails __before__ the change:**
```
1516 ROYDEBUG BEGIN OF 1
...
1518 ROYDEBUG END OF 1
1519 ROYDEBUG BEGIN OF 2
...
3096 AssertionError: False is not true : verify we got "C++ Throw"
```
Look at this diff's V5 for where the "ROYDEBUG" print statements are in the test. This verifies that the verification failed during the 2nd debug session.
See full test output: P1742862144

**Test passes __after__ the change:**
```
[[email protected] ~/llvm-sand/build/Debug/fbcode-x86_64/toolchain]$ bin/llvm-lit -sv /home/royshi/llvm-sand/external/llvm-project/lldb/test/API/tools/lldb-dap/reuseDAP/TestDAP_reuseAdapter.py

Testing Time: 5.12s

Total Discovered Tests: 1
  Passed: 1 (100.00%)
[[email protected] ~/llvm-sand/build/Debug/fbcode-x86_64/toolchain]$
```

Reviewers: jeffreytan, #lldb_team

Reviewed By: jeffreytan

Subscribers: davidayoung, mavitale, jalalonde, #lldb_team

Differential Revision: https://phabricator.intern.facebook.com/D69966150

Tasks: T214613938

Author: royitaqi

lldb/test/API/tools/lldb-dap/reuseDAP/TestDAP_reuseAdapter.py

@@ -37,3 +37,34 @@ def test_basic_reuse(self):
         breakpoint_ids = self.set_source_breakpoints(source, [breakpoint2_line])
         self.continue_to_breakpoints(breakpoint_ids)
         self.dap_server.request_disconnect()
+
+    @skipIfWindows
+    def test_exception_breakopints(self):
+        """
+        Test reuse lldb-dap works across debug sessions.
+        """
+        program = self.getBuildArtifact("a.out")
+
+        # Keep lldb-dap alive for 10 minutes.
+        dapKeepAliveTimeInMS = 10 * 1000 * 60
+        self.build_and_launch(program, disconnectAutomatically=False, keepAliveTimeout=dapKeepAliveTimeInMS)
+
+        response = self.dap_server.request_setExceptionBreakpoints(
+            filters=["cpp_throw", "cpp_catch"]
+        )
+        self.assertTrue(response)
+        self.assertTrue(response["success"])
+        self.continue_to_exception_breakpoint("C++ Throw")
+        self.dap_server.request_disconnect()
+
+        # Second debug session by reusing lldb-dap.
+        self.create_debug_adapter(reuseDapServer=True)
+        self.launch(program)
+
+        response = self.dap_server.request_setExceptionBreakpoints(
+            filters=["cpp_throw", "cpp_catch"],
+        )
+        self.assertTrue(response)
+        self.assertTrue(response["success"])
+        self.continue_to_exception_breakpoint("C++ Throw")
+        self.dap_server.request_disconnect()

lldb/test/API/tools/lldb-dap/reuseDAP/main.cpp

@@ -1,6 +1,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
+#include <stdexcept>
 
 int main(int argc, char const *argv[], char const *envp[]) {
   for (int i = 0; i < argc; ++i)
@@ -10,6 +11,7 @@ int main(int argc, char const *argv[], char const *envp[]) {
   char *cwd = getcwd(NULL, 0);
   printf("cwd = \"%s\"\n", cwd); // breakpoint 1
   free(cwd);
-  cwd = NULL;
-  return 0; // breakpoint 2
+  cwd = NULL; // breakpoint 2
+  throw new std::runtime_error("This is a C++ exception");
+  return 0;
 }