[lldb] Add extended variable support to Get*VariableList.
This patch adds a new flag to the lldb_private::StackFrame API to get variable lists: `include_extended_vars`. This allows ScriptedFrame (and other future synthetic frames) to construct 'fake' variables and return them in the VariableList, so that commands like `fr v` and `SBFrame::GetVariables` can show them to the user as requested.
This patch includes all changes necessary to call the API the new way - I tried to use my best judgement on when to include extended variables or not and leave comments explaining the decision.
As a consequence of producing extended variables, this patch means that ScriptedFrame can produce Variable objects with ValueType that contains a ValueTypeExtendedMask in a high bit. This necessarily complicates some of the switch/case handling in places where we would expect to find such variables, and this patch makes best effort to address all such cases as well. From experience, they tend to show up whenever we're dealing with checking if a Variable is in a specified scope, which means we basically have to check the high bit against some user input saying "yes/no extended variables".
stack-info: PR: https://github.com/llvm/llvm-project/pull/181501, branch: users/bzcheeseman/stack/9
