[Flight] Improve error message when it's not a real Error object (#28327)

Also deals with symbols. Alternative to #28312.

We currently always normalize rejections or thrown values into `Error`
objects. Partly because in prod it'll be an error object and you
shouldn't fork behavior on knowing the value outside a digest. We might
want to even make the message always opaque to avoid being tempted and
then discover in prod that it doesn't work.

However, we do include the message in DEV.

If this is a non-Error object we don't know what the properties mean.
Ofc, we don't want to include too much information in the rendered
string, so we use the general `describeObjectForErrorMessage` helper.
Unfortunately it's pretty conservative about emitting values so it's
likely to exclude any embedded string atm. Could potentially expand it a
bit.

We could in theory try to serialize as much as possible and re-throw the
actual object to allow for inspection to be expanded inside devtools
which is what I plan on for consoles, but since we're normalizing to an
Error this is in conflict with that approach.

DiffTrain build for [a7144f2](a7144f2)

Author: sebmarkbage

compiled/facebook-www/REVISION

@@ -1 +1 @@
-64e755d7374d753c75dc16ba1a4a09ce7b8689dd
+a7144f297c1c6fe457ca30ce6a211ab59feac11e

compiled/facebook-www/ReactDOMTesting-prod.modern.js

@@ -17080,7 +17080,7 @@ Internals.Events = [
 var devToolsConfig$jscomp$inline_1789 = {
   findFiberByHostInstance: getClosestInstanceFromNode,
   bundleType: 0,
-  version: "18.3.0-www-modern-589eead3",
+  version: "18.3.0-www-modern-f74843f1",
   rendererPackageName: "react-dom"
 };
 var internals$jscomp$inline_2160 = {
@@ -17111,7 +17111,7 @@ var internals$jscomp$inline_2160 = {
   scheduleRoot: null,
   setRefreshHandler: null,
   getCurrentFiber: null,
-  reconcilerVersion: "18.3.0-www-modern-589eead3"
+  reconcilerVersion: "18.3.0-www-modern-f74843f1"
 };
 if ("undefined" !== typeof __REACT_DEVTOOLS_GLOBAL_HOOK__) {
   var hook$jscomp$inline_2161 = __REACT_DEVTOOLS_GLOBAL_HOOK__;
@@ -17532,4 +17532,4 @@ exports.useFormState = function (action, initialState, permalink) {
 exports.useFormStatus = function () {
   return ReactCurrentDispatcher$2.current.useHostTransitionStatus();
 };
-exports.version = "18.3.0-www-modern-589eead3";
+exports.version = "18.3.0-www-modern-f74843f1";

compiled/facebook-www/ReactFlightDOMServer-dev.modern.js

@@ -2335,8 +2335,11 @@ if (__DEV__) {
             message = String(error.message); // eslint-disable-next-line react-internal/safe-string-coercion
 
             stack = String(error.stack);
+          } else if (typeof error === "object" && error !== null) {
+            message = "Error: " + describeObjectForErrorMessage(error);
           } else {
-            message = "Error: " + error;
+            // eslint-disable-next-line react-internal/safe-string-coercion
+            message = "Error: " + String(error);
           }
         } catch (x) {
           message =