uSync.Forms 17.2.0 and 18.1.0

Repo: KevinJump/uSync.Forms

Tested the 17.2.0 nightly in a real Umbraco 17.7 site: nested folder import, folder moves, round-trip export, older-format files and path-created folders all behave
uSync.Forms.Complete showed 0.0.0 in the backoffice; the manifest is now built in code from the assembly version, same as uSync.Forms
Changelog: added an upgrade note, forms need exporting once after upgrading or they report as changed on every import
Released v17.2.0 of uSync.Forms and uSync.Forms.Complete to NuGet
Forward ported v17/main into v18/main as a merge commit, keeping the v18 client pins; prerelease.yml now treats v18/main as the main nightly
Tested the v18 nightly on Umbraco 18.2.1 with Forms 18.2.1, same checks
Released v18.1.0 of uSync.Forms and uSync.Forms.Complete to NuGet