Option to run all of file_test under LLDB (#7429)

This is handy when `file_test`'s stack trace fails to report which file
caused the crash.

.vscode/lldb_launch.json

@@ -19,6 +19,24 @@
         "env TEST_TMPDIR=/tmp"
       ]
     },
+    {
+      "type": "lldb-dap",
+      "request": "launch",
+      "name": "file_test (all files) (lldb)",
+      "program": "bazel-bin/toolchain/testing/file_test",
+      "args": [],
+      "debuggerRoot": "${workspaceFolder}",
+      "initCommands": [
+        "command script import external/+llvm_project+llvm-project/llvm/utils/lldbDataFormatters.py",
+        "command script import scripts/lldbinit.py",
+        "settings append target.source-map \".\" \"${workspaceFolder}\"",
+        "settings append target.source-map \"/proc/self/cwd\" \"${workspaceFolder}\"",
+        "settings set escape-non-printables false",
+        "settings set target.max-string-summary-length 10000",
+        "env TEST_TARGET=//toolchain/testing:file_test",
+        "env TEST_TMPDIR=/tmp"
+      ]
+    },
     {
       "type": "lldb-dap",
       "request": "launch",