Previously, adjust_start_col returned nil when completion items had
different start position from lsp textEdit range
This caused the completion to fall back to \k*$ which ignores the
non-keyword characters
Changes:
- adjust_start_col: now returns the minimum start postion among all
items instead of nil
- _lsp_to_complete_items - normalizes the items by adding the gap between
current and minimum start
Fixes: https://github.com/neovim/neovim/issues/37441
36db6ff2c1