BizHawkClient: Add command to get size of memory domain (#4439)

* Mega Man 2: Remove mm2 commands from client if rom size too small

data/lua/connector_bizhawk_generic.lua

@@ -121,6 +121,14 @@ Response:
 
     Expected Response Type: `HASH_RESPONSE`
 
+- `MEMORY_SIZE`  
+    Returns the size in bytes of the specified memory domain.
+
+    Expected Response Type: `MEMORY_SIZE_RESPONSE`
+
+    Additional Fields:
+    - `domain` (`string`): The name of the memory domain to check
+
 - `GUARD`  
     Checks a section of memory against `expected_data`. If the bytes starting
     at `address` do not match `expected_data`, the response will have `value`
@@ -216,6 +224,12 @@ Response:
     Additional Fields:
     - `value` (`string`): The returned hash
 
+- `MEMORY_SIZE_RESPONSE`  
+    Contains the size in bytes of the specified memory domain.
+
+    Additional Fields:
+    - `value` (`number`): The size of the domain in bytes
+
 - `GUARD_RESPONSE`  
     The result of an attempted `GUARD` request.
 
@@ -376,6 +390,15 @@ request_handlers = {
         return res
     end,
 
+    ["MEMORY_SIZE"] = function (req)
+        local res = {}
+
+        res["type"] = "MEMORY_SIZE_RESPONSE"
+        res["value"] = memory.getmemorydomainsize(req["domain"])
+
+        return res
+    end,
+
     ["GUARD"] = function (req)
         local res = {}
         local expected_data = base64.decode(req["expected_data"])