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GH-35143: [R][C++] Fixed shape tensor causes broken build on OSX (#35154)

### Rationale for this change

`std::reinterpret_pointer_cast` was introduced with FixedShapeTensor PR (#34797) but is not available on OSX (see #35143).

### What changes are included in this PR?

This change switches to using `internal::checked_pointer_cast`.

### Are these changes tested?

Change is tested in CI, but should also be verified on crossbow.

### Are there any user-facing changes?

No.
* Closes: #35143

Authored-by: Rok Mihevc <rok@mihevc.org>
Signed-off-by: Dewey Dunnington <dewey@voltrondata.com>