feat(site): separate variable for whole google Font url

This PR simplifies a possible need to import multiple google fonts, so one only needs to change 1 variable @googlefonts
I also put the import url into a separate variable so even the whole url could be changed by only one variable (perhaps needed to use together with googles css2. See #2895 (comment) )

The change is completely backward compatible

src/theme.less

@@ -63,7 +63,7 @@
 
 .loadFonts() {
     & when (@importGoogleFonts) {
-        @import (css) url("@{googleProtocol}fonts.googleapis.com/css2?family=@{googleFontRequest}");
+        @import (css) url("@{googleFontUrl}");
     }
     & when (@importFonts) and not (@fontName = "") {
         each(@fonts, {

src/themes/default/globals/site.variables

@@ -123,7 +123,9 @@
 @googleFontDisplay: "swap";
 
 @googleProtocol: "https://";
-@googleFontRequest: "@{googleFontName}:@{googleFontSizes}&subset=@{googleSubset}&display=@{googleFontDisplay}";
+@googleFonts: "@{googleFontName}:@{googleFontSizes}";
+@googleFontRequest: "@{googleFonts}&subset=@{googleSubset}&display=@{googleFontDisplay}";
+@googleFontUrl: "@{googleProtocol}fonts.googleapis.com/css2?family=@{googleFontRequest}";
 
 @bold: bold;
 @normal: normal;