Fix incorrect case sensitivity in floating-point number parsing methods

[PopSlime]

Summary

The Single.Parse, Single.TryParse, Double.Parse, and Double.TryParse methods are case-insensitive in .NET Core 3.0 and later, when parsing string representations of PositiveInfinity, NegativeInfinity, and NaN.

References

• dotnet/coreclr@b30280d
• Fixing up the Double/Single parsing code to be correct coreclr#20707 (comment)

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/area-system-runtime

[gewarren]

I left a suggestion to try and make it more clear that all of the symbols are compared case insensitively.

[gewarren]

Suggested change

	In .NET Core 3.0 and later, values that are too large to represent are rounded to <xref:System.Double.PositiveInfinity> or <xref:System.Double.NegativeInfinity> as required by the IEEE 754 specification. In prior versions, including .NET Framework, parsing a value that was too large to represent resulted in failure.
	In .NET Core 3.0 and later versions, values that are too large to represent are rounded to <xref:System.Double.PositiveInfinity> or <xref:System.Double.NegativeInfinity> as required by the IEEE 754 specification. In prior versions, including .NET Framework, parsing a value that's too large to represent results in failure.

[gewarren]

Suggested change

The `s` parameter can contain the current culture's <xref:System.Globalization.NumberFormatInfo.PositiveInfinitySymbol%2A?displayProperty=nameWithType>, <xref:System.Globalization.NumberFormatInfo.NegativeInfinitySymbol%2A?displayProperty=nameWithType>, <xref:System.Globalization.NumberFormatInfo.NaNSymbol%2A?displayProperty=nameWithType> (the string comparison is case-insensitive in .NET Core 3.0 and later, but is case-sensitive in prior versions including .NET Framework), or a string of the form:

The `s` parameter can contain the current culture's <xref:System.Globalization.NumberFormatInfo.PositiveInfinitySymbol%2A?displayProperty=nameWithType>, <xref:System.Globalization.NumberFormatInfo.NegativeInfinitySymbol%2A?displayProperty=nameWithType>, or <xref:System.Globalization.NumberFormatInfo.NaNSymbol%2A?displayProperty=nameWithType> symbol. This string comparison is case-insensitive in .NET Core 3.0 and later versions, but is case-sensitive in prior versions including .NET Framework. The `s` parameter can also be a string of the form: