[ci-skip][Feature #18910][lldb] Provide class framework for lldb commands

`lldb_cruby.py` manages lldb custom commands using functions. The file
is a large list of Python functions, and an init handler to map some of
the Python functions into the debugger, to enable execution of custom
logic during a debugging session.

Since LLDB 3.7 (September 2015) there has also been support for using
python classes rather than bare functions, as long as those classes
implement a specific interface.

This PR Introduces some more defined structure to the LLDB helper
functions by switching from the function based implementation to the
class based one, and providing an auto-loading mechanism by which new
functions can be loaded.

The intention behind this change is to make working with the LLDB
helpers easier, by reducing code duplication, providing a consistent
structure and a clearer API for developers.

The current function based approach has some advantages and
disadvantages

Advantages:

- Adding new code is easy.
- All the code is self contained and searchable.

Disadvantages:
- No visible organisation of the file contents. This means
  - Hard to tell which functions are utility functions and which are
    available to you in a debugging session
  - Lots of code duplication within lldb functions
- Large files quickly become intimidating to work with - for example,
  `lldb_disasm.py` was implemented as a seperate Python module because
  it was easier to start with a clean slate than add significant amounts
  of code to `lldb_cruby.py`

This PR attempts, to fix the disadvantages of the current approach and
maintain, or enhance, the benefits. The new structure of a command looks
like this;

 ```
 class TestCommand(RbBaseCommand):
    # program is the keyword the user will type in lldb to execute this command
    program = "test"

    # help_string will be displayed in lldb when the user uses the help functions
    help_string = "This is a test command to show how to implement lldb commands"

    # call is where our command logic will be implemented
    def call(self, debugger, command, exe_ctx, result):
        pass
  ```

If the command fulfils the following criteria it will then be
auto-loaded when an lldb session is started:

- The package file must exist inside the `commands` directory and the
  filename must end in `_command.py`
- The package must implement a class whose name ends in `Command`
- The class inherits from `RbBaseCommand` or at minimum a class that
  shares the same interface as `RbBaseCommand`  (at minimum this means
  defining `__init__` and `__call__`, and using `__call__` to call
  `call` which is defined in the subclasses).
- The class must have a class variable `package` that is a String. This
  is the name of the command you'll call in the `lldb` debugger.

misc/rb_base_command.py

@@ -0,0 +1,68 @@
+import lldb
+from pydoc import locate
+
+class RbBaseCommand:
+    @classmethod
+    def register_lldb_command(cls, debugger, module_name):
+        # Add any commands contained in this module to LLDB
+        command = f"command script add -c {module_name}.{cls.__name__} {cls.program}"
+        debugger.HandleCommand(command)
+
+    def __init__(self, debugger, _internal_dict):
+        self.internal_dict = _internal_dict
+
+    def __call__(self, debugger, command, exe_ctx, result):
+        if not ("RUBY_Qfalse" in globals()):
+            self._lldb_init(debugger)
+
+        self.build_environment(debugger)
+        self.call(debugger, command, exe_ctx, result)
+
+    def call(self, debugger, command, exe_ctx, result):
+        raise NotImplementedError("subclasses must implement call")
+
+    def get_short_help(self):
+        return self.__class__.help_string
+
+    def get_long_help(self):
+        return self.__class__.help_string
+
+    def build_environment(self, debugger):
+        self.target = debugger.GetSelectedTarget()
+        self.process = self.target.GetProcess()
+        self.thread = self.process.GetSelectedThread()
+        self.frame = self.thread.GetSelectedFrame()
+
+    def _append_command_output(self, debugger, command, result):
+        output1 = result.GetOutput()
+        debugger.GetCommandInterpreter().HandleCommand(command, result)
+        output2 = result.GetOutput()
+        result.Clear()
+        result.write(output1)
+        result.write(output2)
+
+    def _lldb_init(self, debugger):
+        target = debugger.GetSelectedTarget()
+        global SIZEOF_VALUE
+        SIZEOF_VALUE = target.FindFirstType("VALUE").GetByteSize()
+
+        value_types = []
+        g = globals()
+
+        imemo_types = target.FindFirstType("enum imemo_type")
+
+        for member in imemo_types.GetEnumMembers():
+            g[member.GetName()] = member.GetValueAsUnsigned()
+
+        for enum in target.FindFirstGlobalVariable("ruby_dummy_gdb_enums"):
+            enum = enum.GetType()
+            members = enum.GetEnumMembers()
+            for i in range(0, members.GetSize()):
+                member = members.GetTypeEnumMemberAtIndex(i)
+                name = member.GetName()
+                value = member.GetValueAsUnsigned()
+                g[name] = value
+
+                if name.startswith("RUBY_T_"):
+                    value_types.append(name)
+        g["value_types"] = value_types