Improve performance of urldecode() and rawurldecode()

[nielsdos]

There are two hot spots on my machines:

1. We copy the string because the internal PHP API works in-place.
2. The conversion of hex characters is slow due to going through the C locale handling.

This patch resolves the first hot spots by introducing 2 new internal APIs that avoid the redundant copy and allocate an empty string upfront. The second hotspot is resolved by having a specialised htoi handler.

For the following benchmark:

$encoded = "Hello%20World%21+This%20is%20a%20test%3A%20%40%23%24%25%5E%26*%28%29";
for ($i=0;$i<2000000;$i++) {
  rawurldecode($encoded);
  urldecode($encoded);
}

On an i7-4790:

Benchmark 1: ./sapi/cli/php x.php
  Time (mean ± σ):     364.8 ms ±   3.7 ms    [User: 359.9 ms, System: 3.3 ms]
  Range (min … max):   359.9 ms … 372.0 ms    10 runs

Benchmark 2: ./sapi/cli/php_old x.php
  Time (mean ± σ):     565.5 ms ±   4.9 ms    [User: 561.8 ms, System: 2.5 ms]
  Range (min … max):   560.7 ms … 578.2 ms    10 runs

Summary
  ./sapi/cli/php x.php ran
    1.55 ± 0.02 times faster than ./sapi/cli/php_old x.php

On an i7-1185G7:

Benchmark 1: ./sapi/cli/php x.php
  Time (mean ± σ):     708.8 ms ±   6.1 ms    [User: 701.4 ms, System: 6.3 ms]
  Range (min … max):   701.9 ms … 722.3 ms    10 runs

Benchmark 2: ./sapi/cli/php_old x.php
  Time (mean ± σ):      1.311 s ±  0.019 s    [User: 1.300 s, System: 0.008 s]
  Range (min … max):    1.281 s …  1.348 s    10 runs

Summary
  ./sapi/cli/php x.php ran
    1.85 ± 0.03 times faster than ./sapi/cli/php_old x.php

[devnexen]

oh my ... that s a lot :)