LibJS: Add TokenType::TemplateLiteral

This is required for template literals - we're not quite there yet, but at
least the parser can now tell us when this token is encountered -
currently this yields "Unexpected token Invalid". Not really helpful.

The character is a "backtick", but as we already have
TokenType::{StringLiteral,RegexLiteral} this seemed like a fitting name.

This also enables syntax highlighting for template literals in the js
REPL and LibGUI's JSSyntaxHighlighter.

Libraries/LibJS/Token.h

@@ -111,6 +111,7 @@ namespace JS {
     __ENUMERATE_JS_TOKEN(SlashEquals)                 \
     __ENUMERATE_JS_TOKEN(StringLiteral)               \
     __ENUMERATE_JS_TOKEN(Switch)                      \
+    __ENUMERATE_JS_TOKEN(TemplateLiteral)             \
     __ENUMERATE_JS_TOKEN(This)                        \
     __ENUMERATE_JS_TOKEN(Throw)                       \
     __ENUMERATE_JS_TOKEN(Tilde)                       \