Table: support initializer list constructor. (#915)

To avoid burdening the user with explicit type construction when using
the library, we can use a constructor that accepts an initializer list
(std::initializer_list). This allows users to pass initializer lists
directly without having to wrap them in
std::vector<std::vector<std::string>>. This resolves the ambiguous case
when the inner list contains only two elements.

Bug:https://github.com/ArthurSonzogni/FTXUI/issues/912

src/ftxui/dom/table_test.cpp

@@ -733,5 +733,17 @@ TEST(TableTest, Merge) {
       screen.ToString());
 }
 
+TEST(TableTest, Issue912) {
+  Table({
+      {"a"},
+  });
+  Table({
+      {"a", "b"},
+  });
+  Table({
+      {"a", "b", "c"},
+  });
+}
+
 }  // namespace ftxui
 // NOLINTEND