Add site.Store and hugo.Store and Shortcode.Store

Closes #13021

hugolib/site.go

@@ -95,6 +95,7 @@ type Site struct {
 	language  *langs.Language
 	languagei int
 	pageMap   *pageMap
+	store     *maps.Scratch
 
 	// The owning container.
 	h *HugoSites
@@ -248,6 +249,7 @@ func NewHugoSites(cfg deps.DepsCfg) (*HugoSites, error) {
 			language:           language,
 			languagei:          i,
 			frontmatterHandler: frontmatterHandler,
+			store:              maps.NewScratch(),
 		}
 
 		if i == 0 {
@@ -614,6 +616,10 @@ func (s *Site) AllRegularPages() page.Pages {
 	return s.h.RegularPages()
 }
 
+func (s *Site) Store() *maps.Scratch {
+	return s.store
+}
+
 func (s *Site) CheckReady() {
 	if s.state != siteStateReady {
 		panic("this method cannot be called before the site is fully initialized")