Avoid allocations in PageParameters.getNamedKeys

PageParameters.getNamedKeys allocates a new TreeSet for every invocation:

	public Set<String> getNamedKeys()
	{
		if ((namedParameters == null) || namedParameters.isEmpty())
		{
			return Collections.emptySet();
		}
		Set<String> set = new TreeSet<>();
		for (NamedPair entry : namedParameters)
		{
			set.add(entry.getKey());
		}
		return Collections.unmodifiableSet(set);
	}

Most of the calls to the method do not actually need the contents of the set. They either check if the set is empty, or check if it contains a given key. The empty checks can directly use the underlying list of named parameters, while the contains checks could use iteration since the number of page parameters is likely limited.

The contains check is roughly 5-10 times faster for reasonably sized page parameters. The empty check is 50 times faster.

Benchmark              Mode  Cnt           Score   Error  Units
Benchmark.newHit      thrpt    2   171106625,173          ops/s
Benchmark.newMiss     thrpt    2   139733394,987          ops/s
Benchmark.newIsEmpty  thrpt    2  1119518738,277          ops/s

Benchmark.oldHit      thrpt    2    25517811,801          ops/s
Benchmark.oldMiss     thrpt    2    25526261,487          ops/s
Benchmark.oldIsEmpty  thrpt    2    29757162,970          ops/s