[KGEN] Rename ArgConvention::ByRef to ArgConvention::InOut, NFC. (#41…

…013)

This aligns the terminology with the modern keyword, we haven't
called it 'byref' for a long time.  We may eventually rename
this again but for now align these.

MODULAR_ORIG_COMMIT_REV_ID: eccdfc1e3620f1483b2435391610a530d6318037

stdlib/src/builtin/builtin_list.mojo

@@ -280,9 +280,9 @@ struct VariadicListMem[
 
     # Provide support for variadics of *inout* arguments.  The reference will
     # automatically be inferred to be mutable, and the !kgen.variadic will have
-    # convention=byref.
+    # convention=inout.
     alias _inout_variadic_type = __mlir_type[
-        `!kgen.variadic<`, Self._mlir_ref_type, `, byref>`
+        `!kgen.variadic<`, Self._mlir_ref_type, `, inout>`
     ]
 
     @always_inline