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ARROW-14518: [Ruby] Add support for Arrow::Array.new([BigDecimal]) (#13377)

This requires bigdecimal 3.1.0 or later for BigDecimal#scale.

Arrow::Array.new([BigDecimal]) detects the max precision and scale
from BigDecimals and creates suitable Arrow::Decimal{128,256}DataType
automatically.

This also truncates given BigDecimal when the specified
Arrow::Decimal{128,256}DataType doesn't have enough and scale. This
still doesn't check precision. If an user specifies data that have too
much precision, the data are used as-is.

Authored-by: Sutou Kouhei <kou@clear-code.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>