[FEATURE] Remove Test Code During Package Installation

[esperecyan]

Is your feature request related to a problem? Please describe.
In Unity packages, custom package tests are not ignored, resulting in them being displayed in the Test Runner.

Describe the solution you'd like
Remove the contents under the asmdef configured with UNITY_INCLUDE_TESTS during package installation.

Describe alternatives you've considered
As a workaround, separate from the UPM package, a package for VPM that has test code removed could be prepared, similar to vrchat-community/ClientSim#55.