gdb: add monitor get mapping

Coxxsrequested to merge
coxxs/ryujinx:gdb-memory-mapping into master

This add the following commands to Gdb Stub:

monitor get mappings
monitor get mappings <address>
monitor get mapping <address>

This is the first time arguments are used in Rcmd, so FindRcmdDelegate is changed to CallRcmdDelegate, to allow it to handle arguments cleanly.

The reply format mimics the same command on Atmosphere.
The forced pagination of monitor get mappings in Atmosphere is not added, as I think it's not needed here.

Edited by Coxxs

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