fmt: insert space in front of `?` for propagation (#6250)

doc/docs.md

@@ -1635,7 +1635,7 @@ propagate the error:
 import net.http
 
 fn f(url string) ?string {
-    resp := http.get(url)?
+    resp := http.get(url) ?
     return resp.text
 }
 ```

vlib/v/fmt/fmt.v

@@ -1136,7 +1136,7 @@ pub fn (mut f Fmt) or_expr(or_block ast.OrExpr) {
 			}
 		}
 		.propagate {
-			f.write('?')
+			f.write(' ?')
 		}
 	}
 }

vlib/v/fmt/tests/optional_propagate_keep.vv

@@ -1,3 +1,3 @@
 fn opt_propagate() ?int {
-	eventual_wrong_int()?
+	eventual_wrong_int() ?
 }

vlib/v/fmt/tests/orm_keep.vv

@@ -14,7 +14,7 @@ fn find_all_customers(db sqlite.DB) []Customer {
 }
 
 fn main() {
-	db := sqlite.connect('customers.db')?
+	db := sqlite.connect('customers.db') ?
 	// select count(*) from Customer
 	nr_customers := sql db {
 		select count from Customer