Reproduction steps:
1. Open the attached project “IndexProject“
2. Enter The Play Mode
3. Observe the Console

Expected result: MemoryExtensions.IndexOf works directly with ReadOnlySpan<> without creating a large number of new allocations
Actual result: IndexOfSlow() is exponentially slower than IndexOfFast()

Reproducible with: 2021.3.22f1, 2022.2.11f1, 2023.1.0b6, 2023.2.0a7
Couldn’t test with: 2020.3.46f1- ”error CS0246: The type or namespace name 'ReadOnlySpan<>' could not be found”

Reproducible on: Windows 10

Note: “IndexOfSlow()” in “Assets/ProblemBehaviour.cs“ uses MemoryExtensions.IndexOf with StringComparison overload creates a large number of allocations which causes a long garbage collection time.