[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/commands/command_template.py

@@ -0,0 +1,25 @@
+# This is a command template for implementing a helper function inside LLDB. To
+# use this file
+#   1. Copy it and rename the copy so it ends with `_command.py`.
+#   2. Rename the class to something descriptive that ends with Command.
+#   3. Change the program variable to be a descriptive command name
+#   4. Ensure you are inheriting from RbBaseCommand or another command that 
+#      implements the same interfact
+
+# This test command inherits from RbBaseCommand which provides access to Ruby
+# globals and utility helpers
+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):
+        # This method will be called once the LLDB environment has been setup.
+        # You will have access to self.target, self.process, self.frame, and 
+        # self.thread
+        # 
+        # This is where we should implement our command logic
+        pass