How to reproduce:
1. Open attached project "MemorySnapshotLeakSampleZip.zip"
2. Open the Package Manager and add a local package from disk; the package is located in the project's root directory(MemorySnapshotLeakPackage).
3. Open the Profiler window and start profiling the Editor while looking at the Memory module(Used total and Mono)
4. From the Menu Bar select Memory Snapshot Test and click the only button in the window that pops up to take memory snapshot
5. Note the memory usage after a snapshot is taken. Each time the snapshot is taken, the Mono memory increases exponentially and does not get cleared.

Expected result: the memory usage stops increasing at around 100-200Mb
Actual result: Mono memory increases exponentially and does not get cleared

Reproducible with: 2018.4.23f1, 2019.1.0a5
Fixed in: 2019.1.0a6 and above

Notes:
The issue is only reproducible on Windows, could not reproduce on macOS
The issue is only reproducible when the package contents are imported as a package
The issue is only reproducible when 'Allow unsafe code' in the package .asmdef is enabled