Initial code to make shadow tables read-only to ordinary SQL. The now

xShadowName method is added to the sqlite3_module object and is used
to identify potential shadow tables.  The SQLITE_PREPARE_SHADOW argument
to sqlite3_prepare_v3() is defined.  It is designed to permit writing to
shadow tables, but is currently an unused placeholder.

FossilOrigin-Name: 31942b3dd3f66eb0d9977bf1cadc2f2d7be7967cce2b55784be0b939dfef1985

ext/misc/completion.c

@@ -468,7 +468,8 @@ static sqlite3_module completionModule = {
   0,                         /* xRename */
   0,                         /* xSavepoint */
   0,                         /* xRelease */
-  0                          /* xRollbackTo */
+  0,                         /* xRollbackTo */
+  0                          /* xShadowName */
 };
 
 #endif /* SQLITE_OMIT_VIRTUALTABLE */