Support string and string builder interpolation handler

[skarllot]

The issue or feature being addressed

• Support string interpolation handler for String and StringBuilder

Details on the issue fix or feature implementation

• Create DefaultInterpolatedStringHandler for supporting high performance string interpolation
• Create AppendInterpolatedStringHandler for supporting high performance string interpolation with StringBuilder
• Create ISpanFormattable to support custom interpolation of an object to a Span
• Create method extensions for StringBuilder to support appending with AppendInterpolatedStringHandler
• Optimize Append method extension for StringBuilder

[skarllot]

Maybe StringBuilder extensions are not useful as "method extensions" because the compiler prefer calling string overload instead of with string interpolation.

[SimonCropp]

Maybe StringBuilder extensions are not useful as "method extensions" because the compiler prefer calling string overload instead of with string interpolation.

yeah, i think make it not an extension and add some docs that explains why

[skarllot]

Maybe StringBuilder extensions are not useful as "method extensions" because the compiler prefer calling string overload instead of with string interpolation.

yeah, i think make it not an extension and add some docs that explains why

You mean removing this and calling as PolyfillExtensions.Append?

[SimonCropp]

yep

[skarllot]

Changes made. Additionally, I've optimized interpolation to use TryFormat method extensions.

[skarllot]

Rebased to latest commit

[SimonCropp]

sorry for the delay. i will deploy this now. should be on nuget in 15