[ios][precompile] move header template to separate-folder

[chrfalch]

A small cleanup to make the directory structure of the header file template when building xcframeworks.

Umbrella and module map templates are now moved into a templates folder in the scripts/iOS-prebuilt folder

Prev PR: https://github.com/facebook/react-native/pull/54838 Next PR: https://github.com/facebook/react-native/pull/54840

Changelog:

[INTERNAL] [FIXED] - Moved iOS prebuild scripts to templates folder.

Test Plan:

Run RNTester with prebuilds

[github-actions[bot]]

Job Summary for Gradle

Test All :: run_fantom_tests

Gradle Root Project	Requested Tasks	Gradle Version	Build Outcome	Build Scan®
react-native-github	:private:react-native-fantom:buildFantomTester	9.0.0	:x:

[github-actions[bot]]

Job Summary for Gradle

Test All :: run_fantom_tests

Gradle Root Project	Requested Tasks	Gradle Version	Build Outcome	Build Scan®
react-native-github	:private:react-native-fantom:buildFantomTester	9.0.0	:x: