This tracks allowing translators to add arbitrary parameter transformations that are applied every time the query is executed.

Usage samples:

• Escape special characters in LIKE patterns (e.g. for StartsWith/EndsWith/Contains). It seems like this is what EF6 does (Incorrect string matching behavior on SQL Server with whitespace patterns #19402 (comment)).
• Convert .NET 0-based string (or array) offsets into 1-based SQL offsets where appropriate.

The transformations would need to be applied before looking up the command in the relational command cache, since the transformation may change the nullability of the parameter (and therefore affect the SQL needed).

Split off from #17598, which is about sniffing parameters and selecting different SQL based on their values (for differences other than nullability). This is only about modifying parameter values.