Fix toDecimalString function

[zvonand]

Fix toDecimalString, fix #52407

Reverts #52450

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[nikitamikhaylov]

Why this function is better than something like this toString(toDecimal(x)) ?

[den-crane]

@nikitamikhaylov

SELECT toDecimalString(toDecimal64(6, 6), 6);
┌─toDecimalString(toDecimal64(6, 6), 6)─┐
│ 6.000000                              │
└───────────────────────────────────────┘

SELECT toString(toDecimal64(6, 6));
┌─toString(toDecimal64(6, 6))─┐
│ 6                           │
└─────────────────────────────┘

see

• toString does not respect output_format_decimal_trailing_zero #30934
• Remove trailing zeros from Decimal serialization #15794 #27680
• TO_CHAR (number) / Printf #34142

[robot-ch-test-poll4]

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