Support the parameterization of the schema name in a SQL Server project

Incoming from https://developercommunity.visualstudio.com/t/Support-the-parameterization-of-the-sche/10824776

> As I understand it, VS supports the parameterization of the database name in a SQL Server Database Project but not the schema name. The additional of this feature / capability would be particularly useful in the follow use-case that I am trying to support - namely the use of a single database with “business project” specific schemas. i.e the solution I am working with supports separate data repositories for each “business project”. The name of the schema that would be created for a specific “business project” will not be known until deployment time and is determined by the business. I can easily support this using sql scripts where the schema name is defined as a SQLCMD variable - but this doesn’t appear to be supported in VS.

No files, tests, or entry points are named. Start by investigating how SQL Server projects currently parameterize database names and SQLCMD variables, then define completion as allowing a schema name to be supplied at deployment time.

Written by the indexing model from the issue text.