debug: make local variables load config configurable

[gremat]

Note though that usage of a LoadConfig is not consistent:

• If debug.vim:s:eval() is called directly, most notably from s:expand_vars() (i.e., when the user tries to expand a variable in the variable window), RPCServer.Eval() is used which currently (i.e., delve@v1.23.0) does not allow to specify a LoadConfig.
• If debug.vim:s:eval() is called from go#debug#Print() (e.g., via :GoDebugPrint), RPCServer.Command() is used and DebuggerCommand is provided with a ReturnInfoLoadConfig. However, those values and the values used in the variables window differ.