feat: add font preloading to reduce fout

Author: julioest

antora-ui/src/partials/head-fonts.hbs

@@ -0,0 +1,6 @@
+<link rel="dns-prefetch" href="https://cppalliance.org">
+<link rel="preconnect" href="https://cppalliance.org" crossorigin>
+<link rel="preload" href="https://cppalliance.org/fonts/NotoSansDisplay.ttf" as="font" type="font/ttf" crossorigin fetchpriority="high" />
+<link rel="preload" href="https://cppalliance.org/fonts/NotoSansDisplay-Italic.ttf" as="font" type="font/ttf"
+  crossorigin fetchpriority="high" />
+<link rel="preload" href="https://cppalliance.org/fonts/NotoSansMono.ttf" as="font" type="font/ttf" crossorigin fetchpriority="high" />

antora-ui/src/partials/head.hbs

@@ -1,4 +1,5 @@
 {{> head-prelude}}
+{{> head-fonts}}
 {{> head-title}}
 {{> head-info}}
 {{> head-styles}}