web/elements: add past-tense submitted formatter to Form (#22900)

Adds `submittedVerb` and `formatSubmittedLabel` to the `Form` base
class, plus a `submittedLabel` per-instance override — the past-tense
counterpart to the `submitVerb` / `submittingVerb` pair already
in place. `ModelForm` swaps in a `savedLabel` ("Changes Saved") when
`instancePk` is set, the same create-vs-edit branch already used by
`saveLabel` and `savingLabel`.

With this in place, `getSuccessMessage()` overrides can read the
"Created X" / "Changes Saved" wording off the formatter instead of
restating the create/update branch in every form.

Closes #22900.

Co-Authored-By: Agent (authentik-i22900-assured-preferred-petunia) <279763771+playpen-agent@users.noreply.github.com>

web/src/elements/forms/Form.ts

@@ -148,6 +148,13 @@ export class Form<T = Record<string, unknown>, D = T>
         id: "form.submit.verb.creating",
     });
 
+    /**
+     * The past-tense verb to use in the default success message, e.g. "Created" or "Updated".
+     */
+    public static submittedVerb: string = msg("Created", {
+        id: "form.submit.verb.created",
+    });
+
     //#region Modal helpers
 
     public [TransclusionChildSymbol] = true;
@@ -240,6 +247,14 @@ export class Form<T = Record<string, unknown>, D = T>
     @property({ type: String, attribute: "submitting-label", useDefault: true })
     public submittingLabel: string | null = null;
 
+    /**
+     * The message shown after the form has been successfully submitted. If not provided,
+     * a default label will be generated based on `submittedVerb` and `verboseName`,
+     * falling back to "Created".
+     */
+    @property({ type: String, attribute: "submitted-label", useDefault: true })
+    public submittedLabel: string | null = null;
+
     @property({ type: String, attribute: "cancel-label", useDefault: true })
     public cancelButtonLabel: string | null = msg("Cancel");
 
@@ -427,6 +442,26 @@ export class Form<T = Record<string, unknown>, D = T>
         });
     }
 
+    /**
+     * An overridable method for formatting the message shown after the form has been
+     * successfully submitted.
+     */
+    protected formatSubmittedLabel(submittedLabel = this.submittedLabel): string {
+        if (submittedLabel) {
+            return submittedLabel;
+        }
+
+        const noun = this.verboseName;
+        const verb = (this.constructor as typeof Form).submittedVerb;
+
+        return noun
+            ? msg(str`${verb} ${noun}`, {
+                  id: "form.submitted.verb-entity",
+                  desc: "The message shown after a form is successfully submitted.",
+              })
+            : verb;
+    }
+
     //#endregion
 
     //#region Public methods

web/src/elements/forms/ModelForm.ts

@@ -70,6 +70,14 @@ export abstract class ModelForm<
         id: "form.submit.saving-changes",
     });
 
+    /**
+     * The message shown after the form has been successfully submitted when
+     * editing an instance, e.g. "Changes Saved".
+     */
+    public static savedLabel: string | null = msg("Changes Saved", {
+        id: "form.submit.changes-saved",
+    });
+
     /**
      * A helper method to create an invoker for editing an instance of this form.
      *
@@ -182,6 +190,16 @@ export abstract class ModelForm<
         return super.formatSubmittingLabel(submittingLabel);
     }
 
+    protected override formatSubmittedLabel(submittedLabel?: string): string {
+        const { savedLabel } = this.constructor as typeof ModelForm;
+
+        if (this.instancePk && savedLabel) {
+            return savedLabel;
+        }
+
+        return super.formatSubmittedLabel(submittedLabel);
+    }
+
     protected override formatHeadline(modifier?: string | null): string {
         modifier ||= this.instancePk ? (this.constructor as typeof ModelForm).modifierLabel : null;