pass global.data.js output to template vars

Templates received only global.vars.js output in vars, while pages
received both global.vars.js and global.data.js output via PageData.vars.
This inconsistency forced every template that needed aggregated data to
re-derive it from the pages array, duplicating logic from global.data.js.

Merging globalDataVars into the globalVars object passed to templateBuilder
makes template vars consistent with how page vars already work.

Author: bcomnes

lib/build-pages/index.js

@@ -276,7 +276,7 @@ export async function buildPagesDirect (src, dest, siteData, _opts) {
         const buildResult = await templateBuilder({
           src,
           dest,
-          globalVars,
+          globalVars: { ...globalVars, ...globalDataVars },
           template,
           pages,
         })