chore: upgrade pnpm@7

[koooge]

Upgrade pnpm to 7 and fix posinstall error.

│ > pnpm run prepack --filter ./packages/* -- --stub
│  ERR_PNPM_NO_SCRIPT  Missing script: prepack
│  ELIFECYCLE  Command failed with exit code 1.
└─ Failed in 358ms
 ELIFECYCLE  Command failed with exit code 1.

[SCasarotto]

Ran into the same issue. Can confirm this branch works.

[mizok]

I think it should be "pnpm --filter ./packages/core run prepack --stub", not "pnpm run prepack --filter ./packages -- --stub".

bc using "pnpm run prepack --filter ./packages -- --stub" give me error when run ./packages/playground/basic dev script