Fix SqlServer snake case - OUTPUT i_n_s_e_r_t_e_d.id

[juliano]

Fixes #1768

Problem

Insert returning on MS SQL Server in SnakeCase mode returns OUTPUT i_n_s_e_r_t_e_d.id

Solution

This PR introduces ExternalIdent.Opinionated, which allows us to define if that should be Renameable or not. It is used in SqlIdiom to identify the opinion and generate the token accordingly. With this change, I could remove the workaround in ExpandingReturning that would return an Ident instead of ExternalIdent

Checklist

• Unit test all changes
• Update README.md if applicable
• Add [WIP] to the pull request title if it's work in progress
• Squash commits that aren't meaningful changes
• Run sbt scalariformFormat test:scalariformFormat to make sure that the source files are formatted

@getquill/maintainers