BREAKING

Fixes https://github.com/prisma/team-orm/issues/1326, closes ORM-310.
This is for Prisma 6. We're merging this to feat/next until we're ready for rebasing that branch into main.

This PR gets rid of custom schema.prisma detection logic for yarn.
Some considerations:

• yarn was something of a unique scenario; for instance, we've never had any custom schema.prisma lookup logic for pnpm workspaces

• Prisma will no longer be able to automatically to climb up the workspace tree to find the schema.prisma file defined in the root of the workspace. E.g., say that the directory tree is

  .
  ├── db
  │   └── schema.prisma
  ├── package.json
  └── packages
      ├── a
      │   └── package.json
      └── b
          └── package.json
  

  and the root package.json is

  {
    "name": "pkg-json-workspace-parent",
    "workspaces": [
      "packages/*"
    ],
    "private": true,
    "prisma": {
      "schema": "./db/schema.prisma"
    }
  }

  which contains the prisma.schema attribute.

  If we're running prisma generate in ./packages/a, we'll no longer climb up to ./package.json, read its prisma.schema attribute, and use ./db/schema.prisma as the default argument for prisma generate --schema <PRISMA_SCHEMA_PATH>.