[QNN-EP] Disable file mapping for embedded cache (#27627)
### Description
File mapping is enabled by default, but when the model contains an
embedded EP context in a node, QNN EP attempts to map the EP context as
a file that doesn't exist. This change is to disable file mapping
entirely if econtext_embed_mode = 1.
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Co-authored-by: calvnguy <calvnguy@qti.qualcomm.com>
Co-authored-by: quic_calvnguy <quic_calvnguy@quic_inc.com>
