Log attributes are truncated by number of bytes not number of characters

[MrAlias]

Similar to #5996, adding an attribute to a log record with the string value こんにちは and an attribute value length of 3 set will result in the attribute value being こ. It should be こんに according to the OTel specification:

• set an attribute value length limit such that for each attribute value:
  • if it is a string, if it exceeds that limit (counting any character in it as 1), SDKs MUST truncate that value, so that its length is at most equal to the limit,

Blocked by #5997 which implements an alternate approach that should be adopted to

opentelemetry-go/sdk/log/record.go

Lines 430 to 466 in 446ee38

	// truncate returns a copy of str truncated to have a length of at most n
	// characters. If the length of str is less than n, str itself is returned.
	//
	// The truncate of str ensures that no valid UTF-8 code point is split. The
	// copy returned will be less than n if a characters straddles the length
	// limit.
	//
	// No truncation is performed if n is less than zero.
	func truncate(str string, n int) string {
	if n < 0 {
	return str
	}
	// cut returns a copy of the s truncated to not exceed a length of n. If
	// invalid UTF-8 is encountered, s is returned with false. Otherwise, the
	// truncated copy will be returned with true.
	cut := func(s string) (string, bool) {
	var i int
	for i = 0; i < n; {
	r, size := utf8.DecodeRuneInString(s[i:])
	if r == utf8.RuneError {
	return s, false
	}
	if i+size > n {
	break
	}
	i += size
	}
	return s[:i], true
	}
	cp, ok := cut(str)
	if !ok {
	cp, _ = cut(strings.ToValidUTF8(str, ""))
	}
	return cp
	}

if it is accepted.