LibRegex: Correctly translate BRE pattern end anchors

Previously we were always choosing the "nothing special" code path, even
if the dollar symbol was at the end of the pattern (and therefore should
have been considered special).

Fix that by actually checking if the pattern end follows, and emitting
the correct instruction if necessary.

Userland/Libraries/LibRegex/RegexParser.cpp

@@ -516,6 +516,20 @@ bool PosixBasicParser::parse_one_char_or_collation_element(ByteCode& bytecode, s
         return true;
     }
 
+    // Dollars are special if at the end of a pattern.
+    if (match(TokenType::Dollar)) {
+        consume();
+
+        // If we are at the end of a pattern, emit an end check instruction.
+        if (match(TokenType::Eof)) {
+            bytecode.empend((ByteCodeValueType)OpCodeId::CheckEnd);
+            return true;
+        }
+
+        // We are not at the end of the string, so we should roll back and continue as normal.
+        back(2);
+    }
+
     // None of these are special in BRE.
     if (match(TokenType::Char) || match(TokenType::Questionmark) || match(TokenType::RightParen) || match(TokenType::HyphenMinus)
         || match(TokenType::Circumflex) || match(TokenType::RightCurly) || match(TokenType::Comma) || match(TokenType::Colon)