Fix CApi tests on S390x (#28074)
### Description
When loading data into tensors from memory buffers from external files,
byteswap it if necessary.
Also add a fix for deleter when byteswapping: keep copy of AllocatorPtr
instead of reference.
### Motivation and Context
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- If it fixes an open issue, please link to the issue here. -->
While trying to setup local s390x CI, I've found 4 more tests that fail
on s390x:
CApiTest.TestLoadModelFromArrayWithExternalInitializerFromFileArray
CApiTest.TestLoadModelFromArrayWithExternalInitializersFromFileArray
CApiTest.TestLoadModelFromArrayWithExternalInitializersFromFileArrayPathRobust
CApiTest.TestLoadModelFromArrayWithExternalInitializersFromFileMmap
