; Fix mid-symbol updating/cycling completion preview

; Fix mid-symbol updating/cycling completion preview

This fixes an issue where 'completion-preview-next-candidate' would
fail to take into account the part of the symbol that follows
point (the suffix) when point is at the middle of a symbol, as well as
a similar issue in 'completion-preview--show' that would manifest with
slow 'completion-at-point-functions'.

* lisp/completion-preview.el (completion-preview-next-candidate)
(completion-preview--show): Use recorded 'completion-preview-end'
position instead of current point.

* test/lisp/completion-preview-tests.el (completion-preview-mid-symbol-cycle):
New test.