Remove unnecessary initialization of create_id in JSON.parse()

[Watson1978]

The create_id has no effect if create_additions is false.

• • create_additions: If set to false, the Parser doesn't create
• additions even if a matching class and create_id was found. This option
• defaults to false.

https://github.com/flori/json/blob/8f7ddba3cd343c2bada3c31c9660c63f0c6df114/ext/json/ext/parser/parser.c#L1758-L1760

So, this PR will remove initialization of create_id when create_additions is false.
This PR will improve JSON.parse() performance about 6%.

Environment

• MacBook Pro (16-inch, 2019)
• macOS 11.1
• Intel Core i9 2.4 GHz
• Ruby 2.7.2

Before

Warming up --------------------------------------
   short_string_json    10.920k i/100ms
    long_string_json    10.326k i/100ms
Calculating -------------------------------------
   short_string_json    107.833k (± 1.1%) i/s -    546.000k in   5.064049s
    long_string_json    103.035k (± 0.9%) i/s -    516.300k in   5.011344s

After

Warming up --------------------------------------
   short_string_json    11.654k i/100ms
    long_string_json    11.021k i/100ms
Calculating -------------------------------------
   short_string_json    115.564k (± 0.7%) i/s -    582.700k in   5.042516s
    long_string_json    109.216k (± 0.6%) i/s -    551.050k in   5.045726s

Test code

require 'benchmark/ips'
require 'json'

short_string_json = {
  "a" => "b" * 23,
  "a" * 23 => "b"
}.to_json.freeze

long_string_json = {
  "a" => "b" * 50,
  "a" * 50 => "b"
}.to_json.freeze

Benchmark.ips do |x|
  x.report("short_string_json") { JSON.parse(short_string_json) }
  x.report("long_string_json") { JSON.parse(long_string_json) }
end

[hsbt]

👍