1875809 - Directly call SubstringKernel in self-hosted code

Status: NEW

(Core :: JavaScript Engine: JIT, task, P3)

Description

[André Bargull [:anba]]

We should try to remove the Substring wrapper function which just forwards to SubstringKernel and instead directly call SubstringKernel in self-hosted code. This requires at least two changes:

1. CacheIR compiling for SubstringKernel needs to handle the case when int32 values are typed as doubles.
2. Warp transpiling SubstringKernel needs to add the Math.max calls which were added bug 1874929. We then need to verify GVN can remove these additional Math.max when SubstringKernel is called from the self-hosted String.prototype.{sustring,substr,slice} functions.