Update raw SQL documentation (interpolated and string)

[divega]

This now produces a parameterized query:

var namePattern = "M%T%";
var matchingPeople= context.People
    .FromSql($"SELECT p.* FROM People AS p WHERE p.Name LIKE {namePattern}");

[divega]

Superseded by #447.

[divega]

Not superseded any more. We need individual issues to assign them.

[anpete]

@divega Should I wait on this in case we make changes?

[roji]

This was done in #1673, closing.