[CL-932] Migrate banner component to OnPush & Signals (#17387)

Migrates the BannerComponent to use computed signals and OnPush.

libs/components/src/banner/banner.component.html

@@ -1,11 +1,11 @@
 <div
   class="tw-flex tw-items-center tw-gap-4 tw-p-2 tw-ps-4 tw-text-main tw-border-transparent tw-bg-clip-padding tw-border-solid tw-border-b tw-border-0"
-  [ngClass]="bannerClass"
+  [class]="bannerClass()"
   [attr.role]="useAlertRole() ? 'status' : null"
   [attr.aria-live]="useAlertRole() ? 'polite' : null"
 >
-  @if (icon(); as icon) {
-    <i class="bwi tw-align-middle tw-text-base" [ngClass]="icon" aria-hidden="true"></i>
+  @if (displayIcon(); as icon) {
+    <i class="bwi tw-align-middle tw-text-base" [class]="icon" aria-hidden="true"></i>
   }
   <!-- Overriding focus-visible color for link buttons for a11y against colored background -->
   <span class="tw-grow tw-text-base [&>button[bitlink]:focus-visible:before]:!tw-ring-text-main">

libs/components/src/banner/banner.component.ts

@@ -1,5 +1,4 @@
-import { CommonModule } from "@angular/common";
-import { Component, OnInit, Output, EventEmitter, input, model } from "@angular/core";
+import { ChangeDetectionStrategy, Component, computed, input, output } from "@angular/core";
 
 import { I18nPipe } from "@bitwarden/ui-common";
 
@@ -13,47 +12,69 @@ const defaultIcon: Record<BannerType, string> = {
   warning: "bwi-exclamation-triangle",
   danger: "bwi-error",
 };
-/**
-  * Banners are used for important communication with the user that needs to be seen right away, but has
-  * little effect on the experience. Banners appear at the top of the user's screen on page load and
-  * persist across all pages a user navigates to.
 
-  * - They should always be dismissible and never use a timeout. If a user dismisses a banner, it should not reappear during that same active session.
-  * - Use banners sparingly, as they can feel intrusive to the user if they appear unexpectedly. Their effectiveness may decrease if too many are used.
-  * - Avoid stacking multiple banners.
-  * - Banners can contain a button or anchor that uses the `bitLink` directive with `linkType="secondary"`.
+/**
+ * Banners are used for important communication with the user that needs to be seen right away, but has
+ * little effect on the experience. Banners appear at the top of the user's screen on page load and
+ * persist across all pages a user navigates to.
+ *
+ * - They should always be dismissible and never use a timeout. If a user dismisses a banner, it should not reappear during that same active session.
+ * - Use banners sparingly, as they can feel intrusive to the user if they appear unexpectedly. Their effectiveness may decrease if too many are used.
+ * - Avoid stacking multiple banners.
+ * - Banners can contain a button or anchor that uses the `bitLink` directive with `linkType="secondary"`.
  */
-// FIXME(https://bitwarden.atlassian.net/browse/CL-764): Migrate to OnPush
-// eslint-disable-next-line @angular-eslint/prefer-on-push-component-change-detection
 @Component({
   selector: "bit-banner",
   templateUrl: "./banner.component.html",
-  imports: [CommonModule, IconButtonModule, I18nPipe],
+  imports: [IconButtonModule, I18nPipe],
   host: {
     // Account for bit-layout's padding
     class:
       "tw-flex tw-flex-col [bit-layout_&]:-tw-mx-8 [bit-layout_&]:-tw-my-6 [bit-layout_&]:tw-pb-6",
   },
+  changeDetection: ChangeDetectionStrategy.OnPush,
 })
-export class BannerComponent implements OnInit {
+export class BannerComponent {
+  /**
+   * The type of banner, which determines its color scheme.
+   */
   readonly bannerType = input<BannerType>("info");
 
-  // passing `null` will remove the icon from element from the banner
-  readonly icon = model<string | null>();
+  /**
+   * The icon to display. If not provided, a default icon based on bannerType will be used. Explicitly passing null will remove the icon.
+   */
+  readonly icon = input<string | null>();
+
+  /**
+   * Whether to use ARIA alert role for screen readers.
+   */
   readonly useAlertRole = input(true);
+
+  /**
+   * Whether to show the close button.
+   */
   readonly showClose = input(true);
 
-  // FIXME(https://bitwarden.atlassian.net/browse/CL-903): Migrate to Signals
-  // eslint-disable-next-line @angular-eslint/prefer-output-emitter-ref
-  @Output() onClose = new EventEmitter<void>();
+  /**
+   * Emitted when the banner is closed via the close button.
+   */
+  readonly onClose = output();
 
-  ngOnInit(): void {
-    if (!this.icon() && this.icon() !== null) {
-      this.icon.set(defaultIcon[this.bannerType()]);
+  /**
+   * The computed icon to display, falling back to the default icon for the banner type.
+   * Returns null if icon is explicitly set to null (to hide the icon).
+   */
+  protected readonly displayIcon = computed(() => {
+    // If icon is explicitly null, don't show any icon
+    if (this.icon() === null) {
+      return null;
     }
-  }
 
-  get bannerClass() {
+    // If icon is undefined, fall back to default icon
+    return this.icon() ?? defaultIcon[this.bannerType()];
+  });
+
+  protected readonly bannerClass = computed(() => {
     switch (this.bannerType()) {
       case "danger":
         return "tw-bg-danger-100 tw-border-b-danger-700";
@@ -64,5 +85,5 @@ export class BannerComponent implements OnInit {
       case "warning":
         return "tw-bg-warning-100 tw-border-b-warning-700";
     }
-  }
+  });
 }