Mark divModInt and friends as INLINE (#19267)

So that we don't get a silly worker `$wdivModInt` and risk inlining
`divModInt#` into `divModInt` or `$wdivModInt`, making both unlikely to
inline at call sites.

Fixes #19267.

There's a spurious metric increase in T12545. That seems entirely due to
shifts in Unique distribution (+5% more `IntMap.$winsert` calls).
The inappropriateness of the acceptance window is tracked in #19414.

Metric Increase:
    T12545