Swapped feature image caption input from mobiledoc to lexical

closes https://github.com/TryGhost/Product/issues/4015

Swapped `<KoenigBasicHtmlInput>` for `<KoenigLexicalEditorInput>`

- added support for passing `class` through to the container `<div>`
- updated caption handler to clean HTML and strip/add surrounding `<p>` as necessary
- added passthrough for `onFocus` prop
- updated styles to force font style inheritance within Koeing's `.kg-prose` class

ghost/admin/app/components/gh-editor-feature-image.hbs

@@ -71,12 +71,11 @@
                         aria-label="Alt text for feature image"
                     >
                 {{else}}
-                    <KoenigBasicHtmlInput
-                        @html={{@caption}}
-                        @placeholder={{if this.captionInputFocused "" "Add a caption to the feature image"}}
-                        @class="gh-editor-feature-image-caption {{if (and @isHidden (not this.captionInputFocused)) "faded"}}"
-                        @name="caption"
-                        @onChange={{@updateCaption}}
+                    <KoenigLexicalEditorInput
+                        class="gh-editor-feature-image-caption {{if (and @isHidden (not this.captionInputFocused)) "faded"}}"
+                        @html={{this.caption}}
+                        @onChangeHtml={{this.setCaption}}
+                        @placeholderText={{if this.captionInputFocused "" "Add a caption to the feature image"}}
                         @onFocus={{fn (mut this.captionInputFocused) true}}
                         @onBlur={{fn (mut this.captionInputFocused) false}}
                     />

ghost/admin/app/components/gh-editor-feature-image.js

@@ -1,8 +1,16 @@
 import Component from '@glimmer/component';
+import cleanBasicHtml from '@tryghost/kg-clean-basic-html';
 import {action} from '@ember/object';
 import {inject as service} from '@ember/service';
 import {tracked} from '@glimmer/tracking';
 
+function hasParagraphWrapper(html) {
+    const domParser = new DOMParser();
+    const doc = domParser.parseFromString(html, 'text/html');
+
+    return doc.body?.firstElementChild?.tagName === 'P';
+}
+
 export default class GhEditorFeatureImageComponent extends Component {
     @service settings;
 
@@ -16,6 +24,21 @@ export default class GhEditorFeatureImageComponent extends Component {
         return !this.canDrop && !this.isHovered && !this.args.forceButtonDisplay;
     }
 
+    get caption() {
+        const content = this.args.caption;
+        if (!content) {
+            return null;
+        }
+        // wrap in a paragraph, so it gets parsed correctly
+        return hasParagraphWrapper(content) ? content : `<p>${content}</p>`;
+    }
+
+    @action
+    setCaption(html) {
+        const cleanedHtml = cleanBasicHtml(html || '', {firstChildInnerContent: true});
+        this.args.updateCaption(cleanedHtml);
+    }
+
     @action
     setUploadedImage(results) {
         if (results[0]) {

ghost/admin/app/components/koenig-lexical-editor-input.hbs

@@ -1,7 +1,10 @@
-<div {{react-render this.ReactComponent props=(hash
-    placeholderText=@placeholderText
-    html=@html
-    onChangeHtml=@onChangeHtml
-    onBlur=@onBlur
-)
-}}></div>
+<div
+    {{react-render this.ReactComponent props=(hash
+        placeholderText=@placeholderText
+        html=@html
+        onChangeHtml=@onChangeHtml
+        onBlur=@onBlur
+        onFocus=@onFocus
+    )}}
+    ...attributes
+></div>

ghost/admin/app/components/koenig-lexical-editor-input.js

@@ -81,6 +81,7 @@ export default class KoenigLexicalEditorInput extends Component {
                                 darkMode={this.feature.nightShift}
                                 onChange={props.onChange}
                                 onBlur={props.onBlur}
+                                onFocus={props.onFocus}
                                 isSnippetsEnabled={false}
                                 singleParagraph={true}
                                 className="koenig-lexical-editor-input"

ghost/admin/app/styles/layouts/editor.css

@@ -641,6 +641,13 @@ body[data-user-is-dragging] .gh-editor-feature-image-dropzone {
     opacity: 1 !important;
 }
 
+.gh-editor-feature-image-caption :is(.koenig-lexical *) {
+    font-size: inherit !important;
+    font-family: inherit !important;
+    line-height: inherit !important;
+    letter-spacing: inherit !important;
+}
+
 .gh-editor-feature-image-caption p {
     margin: 0;
 }