[lldb][Docs] Convert platform packets doc to Markdown (#89913)

As before, script did most of the work, hand edits after that.

There's a lot more we can do dedupe this and the packets doc, this will
come in a follow up PR.

Author: DavidSpickett

lldb/docs/index.rst

@@ -158,6 +158,7 @@ interesting areas to contribute to lldb.
    resources/dataformatters
    resources/extensions
    resources/lldbgdbremote
+   resources/lldbplatformpackets
    resources/caveats
    resources/projects
    Public C++ API <https://lldb.llvm.org/cpp_reference/namespacelldb.html>