Mobile: Minor migration fixes

[cvarley100]

Description

• Add seed migration validation check
• Use correct navigation object in migration

Type of change

• Bug fix (a non-breaking change which fixes an issue)
• Enhancement (a non-breaking change which adds functionality)

How Has This Been Tested?

• Tested on iOS simulator

Checklist:

• My code follows the style guidelines for this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• New and existing unit tests pass locally with my changes
• For changes to mobile that include native code (including React Native modules): I have verified that both iOS and Android successfully build in both Debug and Release modes