Improve performance of encoding Uris

[japplis]

If no encoding occurred for a uri (which is quite often the case), there is no need to convert the StringBuilder to a String, just return the input String.

JMH
Before
Benchmark Mode Cnt Score Error Units
UriParserBenchmark.encode thrpt 25 5814265,085 ▒ 235637,894 ops/s

After
Benchmark Mode Cnt Score Error Units
UriParserBenchmark.encode thrpt 25 6764614,389 ▒ 213170,120 ops/s

16.3% improvement

I've also attached a screenshot of JMC showing that a lot of time of the UriParser.encode is spend in the StringBuilder.toString

Thanks for your contribution to Apache Commons! Your help is appreciated!

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