Fix missing images in editor preview due to wrong links (#31299) (#31393)

Backport #31299

Parse base path and tree path so that media links can be correctly
created with /media/.

Resolves #31294

---------

Co-authored-by: Brecht Van Lommel <brecht@blender.org>

modules/markup/renderer.go

@@ -84,10 +84,10 @@ type RenderContext struct {
 }
 
 type Links struct {
-	AbsolutePrefix bool
-	Base           string
-	BranchPath     string
-	TreePath       string
+	AbsolutePrefix bool   // add absolute URL prefix to auto-resolved links like "#issue", but not for pre-provided links and medias
+	Base           string // base prefix for pre-provided links and medias (images, videos)
+	BranchPath     string // actually it is the ref path, eg: "branch/features/feat-12", "tag/v1.0"
+	TreePath       string // the dir of the file, eg: "doc" if the file "doc/CHANGE.md" is being rendered
 }
 
 func (l *Links) Prefix() string {

modules/structs/miscellaneous.go

@@ -25,7 +25,8 @@ type MarkupOption struct {
 	//
 	// in: body
 	Mode string
-	// Context to render
+	// URL path for rendering issue, media and file links
+	// Expected format: /subpath/{user}/{repo}/src/{branch, commit, tag}/{identifier/path}/{file/dir}
 	//
 	// in: body
 	Context string
@@ -53,7 +54,8 @@ type MarkdownOption struct {
 	//
 	// in: body
 	Mode string
-	// Context to render
+	// URL path for rendering issue, media and file links
+	// Expected format: /subpath/{user}/{repo}/src/{branch, commit, tag}/{identifier/path}/{file/dir}
 	//
 	// in: body
 	Context string