Simplify CharSequenceValueConverter#convertToBoolean

Motivation:
CharSequenceValueConverter#convertToBoolean has a few manual conditionals which can be removed if we use AsciiString.contentEqualsIgnoreCase. Also by comparing an AsciiString to a String we will incur conversions to char that can be avoided if we compare against AsciiString.

Modifications:
- Use AsciiString.contentEqualsIgnoreCase
- Compare against a AsciiString

Result:
Simplified CharSequenceValueConverter#convertToBoolean which favors AsciiString comparison.

codec/src/main/java/io/netty/handler/codec/CharSequenceValueConverter.java

@@ -25,6 +25,7 @@
  */
 public class CharSequenceValueConverter implements ValueConverter<CharSequence> {
  public static final CharSequenceValueConverter INSTANCE = new CharSequenceValueConverter();
+ private static final AsciiString TRUE_ASCII = new AsciiString("true");
 
  @Override
  public CharSequence convertObject(Object value) {
@@ -66,14 +67,7 @@ public CharSequence convertFloat(float value) {
 
  @Override
  public boolean convertToBoolean(CharSequence value) {
- if (value instanceof AsciiString) {
- AsciiString asciiString = (AsciiString) value;
- return asciiString.contentEqualsIgnoreCase("true");
- }
- if (value.length() != 4) {
- return false;
- }
- return Boolean.parseBoolean(value.toString());
+ return AsciiString.contentEqualsIgnoreCase(value, TRUE_ASCII);
  }
 
  @Override