Fix up HTML escaping in Reference Cells table

[cartermp]

This removes some of the HTML escaping in the Reference Cells features table and replaces it with code.

[qinezh]

Open Publishing Build Service: The pull request content has been published and here are some changed files links of this time:

• Docset 1 - core-docs
  https://stage.docs.microsoft.com/en-us/dotnet/core/api/system.componentmodel.composition.primitives.composablepartexception?branch=pr-en-us-1021
  https://stage.docs.microsoft.com/en-us/dotnet/core/api/system.componentmodel.composition.primitives.contractbasedimportdefinition?branch=pr-en-us-1021
  https://stage.docs.microsoft.com/en-us/dotnet/core/api/system.componentmodel.composition.primitives.export?branch=pr-en-us-1021
  Please see 3392 more published files of this docset in report.

Status: Succeeded.
Open Publishing Report.

[stevehoag]

LGTM