docs-bug(Table): Add example with `rowspan`

[hb20007]

Documentation Feedback

There are many useful Table examples in the documentation. However, a common use case that’s missing is how to use rowspan to merge identical cells vertically.

For example, say we have the following data:

const ISOTOPE_DATA: PeriodicElement[] = [
  {position: 1, element: 'Hydrogen', isotope: 'Protium', weight: 1.0078},
  {position: 2, element: 'Hydrogen', isotope: 'Deuterium', weight: 2.0141},
  {position: 3, element: 'Hydrogen', isotope: 'Tritium',  weight: 3.016},
  {position: 4, element: 'Helium', isotope: 'Helium-3', weight: 3.016},
  {position: 5, element: 'Helium', isotope: 'Helium-4', weight: 4.0026},
];

We should be able to use it to create a table like this:

Element	Isotope	Weight
Hydrogen	Protium	1.0078
	Deuterium	2.0141
	Tritium	3.016
Helium	Helium-3	3.016
	Helium-4	4.0026

This is related to #11551, which is similar but for the CdkTable documentation.

Affected documentation page

https://material.angular.dev/components/table/examples