Refactor AISUseGTest.cmake to eliminate FetchContent_Declare duplication

[Copilot]

The sanitizer-aware GTest CMake had two nearly-identical FetchContent_Declare blocks differing only in FIND_PACKAGE_ARGS.

Refactored to a single FetchContent_Declare by conditionally setting _gtest_find_package_args:

if(AIS_USE_SANITIZERS OR AIS_USE_INTEGER_SANITIZER OR AIS_USE_THREAD_SANITIZER)
    set(_gtest_find_package_args "")
else()
    set(_gtest_find_package_args FIND_PACKAGE_ARGS NAMES GTest)
endif()

FetchContent_Declare(
  googletest
  URL https://github.com/google/googletest/releases/download/v1.17.0/googletest-1.17.0.tar.gz
  DOWNLOAD_EXTRACT_TIMESTAMP true
  ${_gtest_find_package_args}
  SYSTEM
)

Part of AIHIPFILE-62

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