sql: fix comparison with SCALAR value

After this patch, SCALAR values will be able to be compared with values
of any other scalar type. The comparison will be done according to the
SCALAR rules, which means boolean values < numeric values < string
values < binary values < uuid values.

Closes #6221

@TarantoolBot document
Title: SCALAR and NUMBER values in SQL

SCALAR values can now be compared with values of any other scalar type,
but cannot be implicitly cast to any other scalar type. This means that
SCALAR values cannot participate in arithmetic, bitwise operations,
concatenation, or functions that, by definition, do not accept SCALAR
values.

NUMBER values now also cannot be implicitly cast to any other numeric
type, which means that NUMBER values cannot participate in arithmetic
and bitwise operations, or in functions that, by definition, do not
accept NUMBER values.