use `FlagSkipXXXCheck` to in types.Context to determine whether to check the string or not

[lcwangchao]

Enhancement

see #47355 for detail

We need to remove SkipUTF8Check, SkipASCIICheck and SkipUTF8MB4Check from stmtctx.StatementContext and move these semantics to types.Context to decouple stmtctx and types package.

[lcwangchao]

/sig sql-infra