Extend regex to support original example from issue #820 and more

The original example from issue #820 was using a dash ('-') as fallback,
however, the regular expression did not accept those. It also didn't
support white space (and many other characters) in the fallback, which
are also supported now, so one can even put e.g. links including label
in the fallback.

umap/static/umap/js/umap.core.js

@@ -134,8 +134,11 @@ L.Util.greedyTemplate = function (str, data, ignore) {
         return value;
     }
 
-    return str.replace(/\{ *([\w_\:\."\|]+) *\}/g, function (str, key) {
+    return str.replace(/\{ *([\w_\:\.\|]+)(?:\|("[^"]*"))? *\}/g, function (str, key, staticFallback) {
         var vars = key.split('|'), value, path;
+        if (staticFallback !== undefined) {
+            vars.push(staticFallback);
+        }
         for (var i = 0; i < vars.length; i++) {
             path = vars[i];
             if (path.startsWith('"') && path.endsWith('"')) value = path.substring(1, path.length -1); // static default value.

umap/static/umap/test/Util.js

@@ -185,6 +185,26 @@ describe('L.Util', function () {
         it('should use the first defined value', function () {
             assert.equal(L.Util.greedyTemplate('A phrase with a {fr.var.bar|try.again|"default"}.', {try: { again: 'again'}, fr: {var: {bar: 'value'}}}), 'A phrase with a value.');
         });
+
+        it('should support the first example from #820 when translated to final syntax', function () {
+            assert.equal(L.Util.greedyTemplate('# {name} ({ele|"-"} m ü. M.)', {name: 'Portalet'}), '# Portalet (- m ü. M.)');
+        });
+
+        it('should support the first example from #820 when translated to final syntax when no fallback required', function () {
+            assert.equal(L.Util.greedyTemplate('# {name} ({ele|"-"} m ü. M.)', {name: 'Portalet', ele: 3344}), '# Portalet (3344 m ü. M.)');
+        });
+
+        it('should support white space in fallback', function () {
+            assert.equal(L.Util.greedyTemplate('A phrase with {var|"white space in the fallback."}', {}), 'A phrase with white space in the fallback.');
+        });
+
+        it('should support empty string as fallback', function () {
+            assert.equal(L.Util.greedyTemplate('A phrase with empty string ("{var|""}") in the fallback.', {}), 'A phrase with empty string ("") in the fallback.');
+        });
+
+        it('should support e.g. links as fallback', function () {
+            assert.equal(L.Util.greedyTemplate('A phrase with {var|"[[https://osm.org|link]]"} as fallback.', {}), 'A phrase with [[https://osm.org|link]] as fallback.');
+        });
     });
 
     describe('#TextColorFromBackgroundColor', function () {