[lldb] Add matching based on Python callbacks for data formatters.

This patch adds a new matching method for data formatters, in addition
to the existing exact typename and regex-based matching. The new method
allows users to specify the name of a Python callback function that
takes a `SBType` object and decides whether the type is a match or not.

Here is an overview of the changes performed:

- Add a new `eFormatterMatchCallback` matching type, and logic to handle
  it in `TypeMatcher` and `SBTypeNameSpecifier`.

- Extend `FormattersMatchCandidate` instances with a pointer to the
  current `ScriptInterpreter` and the `TypeImpl` corresponding to the
  candidate type, so we can run registered callbacks and pass the type
  to them. All matcher search functions now receive a
  `FormattersMatchCandidate` instead of a type name.

- Add some glue code to ScriptInterpreterPython and the SWIG bindings to
  allow calling a formatter matching callback. Most of this code is
  modeled after the equivalent code for watchpoint callback functions.

- Add an API test for the new callback-based matching feature.

For more context, please check the RFC thread where this feature was
originally discussed:
https://discourse.llvm.org/t/rfc-python-callback-for-data-formatters-type-matching/64204/11

Differential Revision: https://reviews.llvm.org/D135648

lldb/source/Plugins/ScriptInterpreter/Python/ScriptInterpreterPython.cpp

@@ -2154,6 +2154,14 @@ bool ScriptInterpreterPythonImpl::GetScriptedSummary(
   return ret_val;
 }
 
+bool ScriptInterpreterPythonImpl::FormatterCallbackFunction(
+    const char *python_function_name, TypeImplSP type_impl_sp) {
+  Locker py_lock(this,
+                 Locker::AcquireLock | Locker::InitSession | Locker::NoSTDIN);
+  return LLDBSwigPythonFormatterCallbackFunction(
+      python_function_name, m_dictionary_name.c_str(), type_impl_sp);
+}
+
 bool ScriptInterpreterPythonImpl::BreakpointCallbackFunction(
     void *baton, StoppointCallbackContext *context, user_id_t break_id,
     user_id_t break_loc_id) {