Reduce overhead of unsampled requests

[trask]

#3678 shows that HandlerMappingResourceNameFilter.findMapping is expensive, so easy win to hide it behind isRecording check

Benchmark                                                               Score       Error   Units
ServletBenchmark.execute                                              105.731 ±     0.066   us/op
ServletBenchmark.execute:execute·p0.50                                102.272               us/op
ServletBenchmark.execute:·gc.alloc.rate.norm                        47349.318 ± 12700.246    B/op
ServletWithAgentDisabledBenchmark.execute                              90.191 ±     0.058   us/op
ServletWithAgentDisabledBenchmark.execute:execute·p0.50                87.552               us/op
ServletWithAgentDisabledBenchmark.execute:·gc.alloc.rate.norm       44087.647 ± 11458.853    B/op
ServletWithNoopApiBenchmark.execute                                   100.375 ±     0.062   us/op
ServletWithNoopApiBenchmark.execute:execute·p0.50                      97.024               us/op
ServletWithNoopApiBenchmark.execute:·gc.alloc.rate.norm             46146.656 ± 12239.658    B/op
ServletWithOnePercentSamplingBenchmark.execute                        103.976 ±     0.065   us/op
ServletWithOnePercentSamplingBenchmark.execute:execute·p0.50          100.608               us/op
ServletWithOnePercentSamplingBenchmark.execute:·gc.alloc.rate.norm  46809.705 ± 12494.367    B/op

after:

Benchmark                                                               Score       Error   Units
ServletBenchmark.execute                                              105.396 ±     0.066   us/op
ServletBenchmark.execute:execute·p0.50                                102.144               us/op
ServletBenchmark.execute:·gc.alloc.rate.norm                        47354.717 ± 12704.220    B/op
ServletWithAgentDisabledBenchmark.execute                              90.639 ±     0.059   us/op
ServletWithAgentDisabledBenchmark.execute:execute·p0.50                88.064               us/op
ServletWithAgentDisabledBenchmark.execute:·gc.alloc.rate.norm       44008.361 ± 11427.639    B/op
ServletWithNoopApiBenchmark.execute                                    97.427 ±     0.060   us/op
ServletWithNoopApiBenchmark.execute:execute·p0.50                      94.592               us/op
ServletWithNoopApiBenchmark.execute:·gc.alloc.rate.norm             45225.107 ± 11889.072    B/op
ServletWithOnePercentSamplingBenchmark.execute                        101.981 ±     0.063   us/op
ServletWithOnePercentSamplingBenchmark.execute:execute·p0.50           99.072               us/op
ServletWithOnePercentSamplingBenchmark.execute:·gc.alloc.rate.norm  45918.495 ± 12155.446    B/op