feat: fluent.syntax

Портирование кода из fluent-kotlin
https://github.com/projectfluent/fluent-kotlin

fluent.syntax/src/test/resources/reference_fixtures/select_expressions.ftl

@@ -0,0 +1,64 @@
+new-messages =
+    { BUILTIN() ->
+        [0] Zero
+       *[other] {""}Other
+    }
+
+valid-selector-term-attribute =
+    { -term.case ->
+       *[key] value
+    }
+
+# ERROR Term values are not valid selectors
+invalid-selector-term-value =
+    { -term ->
+       *[key] value
+    }
+
+# ERROR CallExpressions on Terms are similar to TermReferences
+invalid-selector-term-variant =
+    { -term(case: "nominative") ->
+       *[key] value
+    }
+
+# ERROR Nested expressions are not valid selectors
+invalid-selector-nested-expression =
+    { { 3 } ->
+        *[key] default
+    }
+
+# ERROR Select expressions are not valid selectors
+invalid-selector-select-expression =
+    { { $sel ->
+        *[key] value
+        } ->
+        *[key] default
+    }
+
+empty-variant =
+    { $sel ->
+       *[key] {""}
+    }
+
+reduced-whitespace =
+    {FOO()->
+       *[key] {""}
+    }
+
+nested-select =
+    { $sel ->
+       *[one] { $sel ->
+          *[two] Value
+       }
+    }
+
+# ERROR Missing selector
+missing-selector =
+    {
+       *[key] Value
+    }
+
+# ERROR Missing line end after variant list
+missing-line-end =
+    { $sel ->
+        *[key] Value}