[InstCombine] improve matching for sext-lshr-trunc patterns, part 2

Similar to rG42f488b63a04

This is intended to preserve the logic of the existing transform,
but remove unnecessary restrictions on uses and types.

https://rise4fun.com/Alive/oS0

  Name: narrow input
  Pre: C1 <= width(C1) - 24
  %B = sext i8 %A
  %C = lshr %B, C1
  %r = trunc %C to i24
  =>
  %s = ashr i8 %A, trunc(umin(C1, 7))
  %r = sext i8 %s to i24

  Name: wide input
  Pre: C1 <= width(C1) - 24
  %B = sext i24 %A
  %C = lshr %B, C1
  %r = trunc %C to i8
  =>
  %s = ashr i24 %A, trunc(umin(C1, 23))
  %r = trunc i24 %s to i8