[EPIC] change SQL numeric literals from float to decimal

[kmitchener]

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Currently DataFusion interprets all non-integer numeric literals as floats, but they should be decimals instead.

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List of related issues. Probably all of these should be fixed before the actual switch to decimals is committed.

• panic at attempt to multiply with overflow when doing math on Decimal128 columns #3437
• add support for casting string to decimal #3478
• coercion between decimal and other types lacking, compared to other numeric types #3479
• comparison operations with a scalar null and decimal array panics #3487
• Floating value literals without postfix should be parsed as decimal #4072
• change SQL non-integer numeric literal type from Float64 to Decimal128 #3394
• The percentile argument for ApproxPercentileCont must be Float64, not Decimal128(2, 1) #4103