Add example with input group between two inputs

[vanillajonathan]

This adds an example to the documentation that illustrates the usage of a input group between two inputs.

This is related to feature request #25120.

It can be used for example:

Input	Form
Dimensions	[width][x][height]
Time	[hour][:][minutes]
Month & year	[mm][/][yyyy]
Range	[1000][–][9999]
Username on host	[username][@][server]