Rework MODE/RPL_CHANMODEIS handling for trailing args (#1661)

Some servers may send a colon even if the last parameter doesn't need it, currently this leads to issues with permission/mode tracking, as the core doesn't handle the colon properly.

This fix replaces reconstructing the parameter string with just passing a vector of the relevant parameters to CChan::SetModes() and adds overrides for CChan::SetModes() and CChan::ModeChange() that accept the vector instead.

Clean up uses of old CModeMessage::GetModes()

src/Message.cpp

@@ -267,3 +267,23 @@ void CMessage::InitType() {
         }
     }
 }
+
+VCString CMessage::GetParamsSplit(unsigned int uIdx, unsigned int uLen) const {
+    VCString splitParams;
+    const VCString &params = GetParams();
+
+    if (params.empty() || uLen == 0 || uIdx >= params.size()) {
+        return splitParams;
+    }
+
+    if (uLen > params.size() - uIdx - 1) {
+        uLen = params.size() - uIdx;
+    }
+
+    VCString::const_iterator startIt = params.begin() + uIdx;
+    VCString::const_iterator endIt = startIt + uLen;
+
+    splitParams.assign(startIt, endIt);
+
+    return splitParams;
+}