Update template to gitignore android/app/.cxx (#34430)

Summary:
CMake gens running debug
- `android/app/.cxx/Debug/*`
- `android/app/.cxx/RelWithDebInfo/*`

Neither/nothing during release.

So probably want the 87 debug files untracked.

Follow-up: #34354

_macOS 13b, RN 0.70.0-rc.3_

## Changelog

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[Android] [Added] - Update template to gitignore `android/app/.cxx`

Pull Request resolved: #34430

Test Plan: Everything builds and runs as expected

Reviewed By: cipolleschi

Differential Revision: D38752097

Pulled By: cortinico

fbshipit-source-id: 61c31317d5e45f831445841f3e14da871b3903e5

Author: leotm

template/_gitignore

@@ -30,6 +30,7 @@ build/
 local.properties
 *.iml
 *.hprof
+.cxx/
 
 # node.js
 #