build: include bin files needed for v8_context_snapshot_generator

[jkleinsc]

Description of Change

v8_context_snapshot_generator needs natives_blob.bin and snapshot_blob.bin to properly run. Those could be copied from an Electron build, but adding them to the mksnapshot dist will allow v8_context_snapshot_generator to run without the user having to find and copy those bin files. Additionally this change will make sure that the 3-0-x mksnapshot zip contents match what is provided in 4-0-x and higher

Checklist

• [x] PR description included and stakeholders cc'd
• [x] script/update runs without error
• [x] PR title follows semantic commit guidelines