Update Complex.ToString to reflect formatting in .NET 8+ (#10125)

Per dotnet/docs#41835, the format from Complex.ToString changed in .NET 8 from (a, b) to <a; b>

Author: jeffhandley

xml/System.Numerics/Complex.xml

@@ -6816,7 +6816,7 @@ Languages that support custom operators can use the <xref:System.Numerics.Comple
           <format type="text/markdown"><![CDATA[
 
 ## Remarks
- The default string representation of a complex number displays the number using its Cartesian coordinates in the form `(`*a*`,` *b*`)`, where *a* is the real part of the complex number, and *b* is its imaginary part. Both *a* and *b* are formatted using the general format specifier ("G") and the conventions of the current system culture.
+ The default string representation of a complex number displays the number using its Cartesian coordinates in the form `<`*a*`;` *b*`>`, where *a* is the real part of the complex number, and *b* is its imaginary part. Both *a* and *b* are formatted using the general format specifier ("G") and the conventions of the current system culture.
 
 
 
@@ -6889,7 +6889,7 @@ Languages that support custom operators can use the <xref:System.Numerics.Comple
           <format type="text/markdown"><![CDATA[
 
 ## Remarks
- The string representation of the complex number returned by this method displays the number using its Cartesian coordinates in the form `(`*a*`,` *b*`)`, where *a* is the real part of the complex number, and *b* is its imaginary part. Both *a* and *b* are formatted using the general format specifier ("G") and the conventions of the culture defined by `provider`.
+ The string representation of the complex number returned by this method displays the number using its Cartesian coordinates in the form `<`*a*`;` *b*`>`, where *a* is the real part of the complex number, and *b* is its imaginary part. Both *a* and *b* are formatted using the general format specifier ("G") and the conventions of the culture defined by `provider`.
 
  The `provider` parameter is an <xref:System.IFormatProvider> implementation. Its <xref:System.IFormatProvider.GetFormat%2A> method returns a <xref:System.Globalization.NumberFormatInfo> object that provides culture-specific information about the format of the real and imaginary numbers in the returned string. If `provider` is `null`, the returned string is formatted using the <xref:System.Globalization.NumberFormatInfo> object of the current culture.
 
@@ -6976,7 +6976,7 @@ Languages that support custom operators can use the <xref:System.Numerics.Comple
           <format type="text/markdown"><![CDATA[
 
 ## Remarks
- The string representation of the complex number returned by this method displays the number using its Cartesian coordinates in the form `(`*a*`,` *b*`)`, where *a* is the real part of the complex number, and *b* is its imaginary part. Both *a* and *b* are formatted using the format string specified by `format`. The `format` parameter can be any valid standard numeric format specifier, or any combination of custom numeric format specifiers. If `format` is equal to <xref:System.String.Empty?displayProperty=nameWithType> or is `null`, the real and imaginary parts of the complex number are formatted with the general format specifier ("G"). If `format` is any other value, the method throws a <xref:System.FormatException>.
+ The string representation of the complex number returned by this method displays the number using its Cartesian coordinates in the form `<`*a*`;` *b*`>`, where *a* is the real part of the complex number, and *b* is its imaginary part. Both *a* and *b* are formatted using the format string specified by `format`. The `format` parameter can be any valid standard numeric format specifier, or any combination of custom numeric format specifiers. If `format` is equal to <xref:System.String.Empty?displayProperty=nameWithType> or is `null`, the real and imaginary parts of the complex number are formatted with the general format specifier ("G"). If `format` is any other value, the method throws a <xref:System.FormatException>.
 
  The .NET Framework provides extensive formatting support, which is described in greater detail in the following topics:
 
@@ -7066,7 +7066,7 @@ Languages that support custom operators can use the <xref:System.Numerics.Comple
           <format type="text/markdown"><![CDATA[
 
 ## Remarks
- The string representation of the complex number returned by this method displays the number using its Cartesian coordinates in the form `(`*a*`,` *b*`)`, where *a* is the real part of the complex number, and *b* is its imaginary part. Both *a* and *b* are formatted using the format string specified by `format`. The `format` parameter can be any valid standard numeric format specifier, or any combination of custom numeric format specifiers. If `format` is equal to <xref:System.String.Empty?displayProperty=nameWithType> or is `null`, the real and imaginary parts of the complex number are formatted with the general format specifier ("G"). If `format` is any other value, the method throws a <xref:System.FormatException>.
+ The string representation of the complex number returned by this method displays the number using its Cartesian coordinates in the form `<`*a*`;` *b*`>`, where *a* is the real part of the complex number, and *b* is its imaginary part. Both *a* and *b* are formatted using the format string specified by `format`. The `format` parameter can be any valid standard numeric format specifier, or any combination of custom numeric format specifiers. If `format` is equal to <xref:System.String.Empty?displayProperty=nameWithType> or is `null`, the real and imaginary parts of the complex number are formatted with the general format specifier ("G"). If `format` is any other value, the method throws a <xref:System.FormatException>.
 
  The .NET Framework provides extensive formatting support, which is described in greater detail in the following topics: