Auto merge of #103185 - chenyukang:yukang/fix-span-next-point, r=davidtwco

Fix the bug of next_point in source_map

There is a bug in `next_point`, the new span won't move to next position when be called in the first time.

For this reason, our current code is working like this:
1. When we really want to move to the next position, we called two times of `next_point`
2. Some code which use `next_point` actually done the same thing with `shrink_to_hi`

This fix make sure when `next_point` is called, span will move with the width at least 1, and also work correctly in the scenario of multiple bytes.

Ref: rust-lang/rust#103140 (comment)

r? `@davidtwco`

Author: bors