[C++] Introduce simdjson and migrate ObjectParser #50566

Describe the enhancement requested

Introduce simdjson into Arrow and migrate arrow::json::internal::ObjectParser from RapidJSON to simdjson.

Scope:

• Add simdjson as a supported dependency.
• Integrate simdjson with the Arrow build system.
• Migrate ObjectParser to simdjson.
• Add or update tests for the migrated implementation.

Parent issue: #35460

Component(s)

C++