SSDT is stuck on 162.x.x of DacFx, while VS 2026 ships with 170.x.x - making custom contributors/deployment modifiers unusable in VS

Nobody has claimed this yet.

- SqlPackage or DacFx Version: `162.5.57` in SSDT/Contributor, `170.4.53` in VS 2026 `18.7.0`
- .NET Framework (Windows-only) or .NET Core: `Net472`/`NetStandard2.0`
- Environment (local platform and source/target platforms): Locally running Windows with VS 2026 `18.7.0`, Sqlproj targeting various levels of sql compatibility, Contributor using `162.5.57` of DacFx

**Steps to Reproduce:**

1. Create a sqlproj project
2. Create a contributor
3. Reference the contributor in the sql project
4. Copy assemblies for contributor to extensions folder for VS (i.e. `C:\Program Files\Microsoft Visual Studio\18\Enterprise\Common7\IDE\Extensions\Microsoft\SQLDB\DAC`)
5. Build the project, notice an error about DacFx version but project still builds and contributor files (if any) still get added to dacpac. Error is as follows:
```
Could not load extensions from file 'C:\Program Files\Microsoft Visual Studio\18\Enterprise\Common7\IDE\Extensions\Microsoft\SQLDB\DAC\Extensions\xxx.dll' because the assembly has dependency to older versions of DacFx. For more information check https://aka.ms/sqlprojects-extensions
```
6. Try to publish the project in Visual Studio - Contributor is ignored entirely.
7. If one tries to upgrade to 170.x.x of DacFx for the contributor and copy the files to the Extensions folder, the project will NOT build as SSDT does not support it. So this means that currently SSDT with a custom Contributor is currently *broken* in VS 2026 entirely. We can still build, our CICD pipelines still work as they use sqlpackage.exe, but this really impacts our developers' experience with the tooling.

**Did this occur in prior versions? If not - which version(s) did it work in?**

I am actually not sure when it broke in VS 2026 - I only noticed it after a developer on my team brought to my attention the inability to publish correctly. I know there was no issues in VS 2022. So it broke whenever VS 2026 upgraded to 170.x.x version of DacFx. Screenshot below from VS install folder shows 170.x.x in use.

Start with the sqlproj contributor loading path and the SSDT extension folder at C:\Program Files\Microsoft Visual Studio\18\Enterprise\Common7\IDE\Extensions\Microsoft\SQLDB\DAC. Reproduce the build and publish steps using DacFx 162.5.57 versus 170.4.53, then trace how the dependency version is validated. Done means a custom contributor loads and is honored during VS 2026 publish without the DacFx version error.

Written by the indexing model from the issue text.