webnn: Disable CFI on functions which call into a shared library

This change disables CFI indirection function call checking for the
files which make calls to a TFLiteDelegate, as it could be provided by
a shared library.

Using the GPU delegate from the Optimization Guide library can now be
re-enabled.

Bug: 394119734, 396748132
Change-Id: I1cc6fb8c180663f56b8da6622a4aa78d6fcc9581
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6282768
Reviewed-by: Peter Collingbourne <pcc@chromium.org>
Commit-Queue: Reilly Grant <reillyg@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1422323}
NOKEYCHECK=True
GitOrigin-RevId: 20dfea70bef5740e4155df6b1e9ab2376bbc9eb4