refactor types package to decouple it from stmtctx

[lcwangchao]

Enhancement

Currently, the package types methods rely on the package stmtctx as the context for value conversion. We'd better to
avoid it and decouple these two packages for some reasons:

• types is a basic package, it should not have an assumption that all the value operations happen in a statement of SQL.
• stmtctx.StatementContext has too many fields and is challenging to use. We should a simple object for context with clear semantics

For above reasons, we should redesign the context in package to introduce a new context named types.Context . For example:

type Context struct {
    flags Flags
    loc *time.Location
    warningFunc func(err)
}

The new context definition has some fields:

• flags: some flags to indicate how to handle the value conversion.
• loc: the timezone info, it will be used by some time-related functions.
• warningFunc: in some cases, we only want to append a warning to somewhere instead of returning an error. This function will be called when an error happens and the context indicates to enable warnings.

It's better to make the Context as immutable to make it thread-safe and easier to use. So the inner fields are designed to be private.

The Flags type will be defined as an int with each bit stands for a flag:

const (
	FlagIgnoreTruncateErr Flags = 1 << iota
	FlagTruncateAsWarning
	FlagClipNegativeToZero
	FlagIgnoreOverflowError
	FlagOverflowAsWarning
	FlagIgnoreZeroDateErr
	FlagZeroDateAsWarning
	FlagIgnoreZeroInDateErr
	FlagZeroInDateAsWarning
	FlagIgnoreInvalidDateErr
	FlagInvalidDateAsWarning
	FlagSkipASCIICheck
	FlagSkipUTF8Check
	FlagSkipUTF8MB4Check
)

sub tasks

• redefine context used by types package #47478
• use FlagSkipXXXCheck to in types.Context to determine whether to check the string or not #47479
• move time zone info in stmtctx.StatementContext into TypeCtx #47590
• Make types.StrictFlags more strict #47829
• use ZeroDate related flags to handle some in functions in types package #47507
• use ZeroInDate and InvalidDate related flags to handle cases in functions in types package #47508
• always return overflow error for the functions in types package #47517
• use FlagClipNegativeToZero to handle clip to zero case in types package #47518
• use truncated related flags to handle truncte cases in types package #47511
• remove param explicitTz from types.ParseTime #48573
• Remove the dependency stmtctx from pkg/util/dbutil #48911
• Use interface rather than closure in *ctx to remove memory allocation #49277
• Refractor the way to handle error and warning #48611
• remove stmtctx dependency from tablecodec and rowcodec #48751
• stmtctx: remove OverflowAsWarning flag #49122

[YangKeao]

Maybe it's time to remove all (or as most as possible) stmtctx from types. Let's do it! #48080

[bb7133]

Can we close this issue now?

[lcwangchao]

Can we close this issue now?

#49122 is still in review. Maybe we can close it after it finished.