[StackFrame] Add more clarifying comments to StackFrameList (NFC)
[StackFrame] Add more clarifying comments to StackFrameList (NFC)

git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@339205 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit 9acd265ae3803fdf8b53273aae9bff6ef39caa99)

apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb