Reverts #140478
Initiated by: loic-sharma
This change reverts the following previous change:
Original Description:

1. Change templates to IPHONEOS_DEPLOYMENT_TARGET, MinimumOSVersion, and Podfile platform :ios to 12.0.
2. Add migrator for Podfile part to migrate platform :ios, '11.0' -> platform :ios, '12.0'
3. Compile with -miphoneos-version-min=12.0
4. Run the migrator on all example apps and integration tests.

See also #62902 and #85174 and #101963

Fixes #136060

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