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:
```php
$encoded = "Hello%20World%21+This%20is%20a%20test%3A%20%40%23%24%25%5E%26*%28%29";
for ($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
```
Closes GH-18378.
6c0578d31c