ddl: Fix default value filling with finer granularity (#10682)#10687

JaySon-Huang merged 7 commits intopingcap:release-7.5-20260128-v7.5.3pingcap/tiflash:release-7.5-20260128-v7.5.3from

ti-chi-bot:cherry-pick-10682-to-release-7.5-20260128-v7.5.3ti-chi-bot/tiflash:cherry-pick-10682-to-release-7.5-20260128-v7.5.3Copy head branch name to clipboard