Prefer explicit construction to coercion in record initialization

While we support initializing records via coercion from an expression
list, e.g.,

    local x: X = [$x1=1, $x2=2];

this can sometimes obscure the code to readers, e.g., when assigning to
value declared and typed elsewhere. The language runtime has a similar
overhead since instead of just constructing a known type it needs to
check at runtime that the coercion from the expression list is valid;
this can be slower than just writing the readible code in the first
place, see #4559.

With this patch we use explicit construction, e.g.,

    local x = X($x1=1, $x2=2);

scripts/policy/protocols/http/detect-webapps.zeek

@@ -29,7 +29,7 @@ event signature_match(state: signature_state, msg: string, data: string) &priori
 
 	local c = state$conn;
 	local si: Software::Info;
-	si = [$name=msg, $unparsed_version=msg, $host=c$id$resp_h, $host_p=c$id$resp_p, $software_type=WEB_APPLICATION];
+	si = Software::Info($name=msg, $unparsed_version=msg, $host=c$id$resp_h, $host_p=c$id$resp_p, $software_type=WEB_APPLICATION);
 	si$url = build_url_http(c$http);
 	Software::found(c$id, si);
 	}