[visual-markdown-editor] Support for images for in project files

GitOrigin-RevId: 488ebcfc6429cfa2ce4f919f8c736822c80fdca1

services/web/frontend/js/features/source-editor/extensions/doc-folder.ts

@@ -0,0 +1,23 @@
+import {
+  Compartment,
+  Extension,
+  Facet,
+  TransactionSpec,
+} from '@codemirror/state'
+
+const docFolderConf = new Compartment()
+
+/**
+ * Folder of the open document (null at the project root), for resolving
+ * document-relative file paths.
+ */
+export const docFolderFacet = Facet.define<string | null, string | null>({
+  combine: values => values[0] ?? null,
+})
+
+export const docFolder = (docFolder: string | null): Extension =>
+  docFolderConf.of(docFolderFacet.of(docFolder))
+
+export const setDocFolder = (docFolder: string | null): TransactionSpec => ({
+  effects: docFolderConf.reconfigure(docFolderFacet.of(docFolder)),
+})