Support static xcframework packaging in build-xcframework.sh (#3322)

Support static xcframework packaging in build-xcframework.sh (#3322)

* This commit allows for the building of a static xcframework by adding a
BUILD_STATIC_XCFRAMEWORK option. When enabled, the build-xcframework.sh
script builds a self-contained static whisper.xcframework.

The motivation for this change is so that command line binaries can link
whisper.cpp without forcing users to install the whisper.xcframework
separately.

* Update build-xcframework.sh

Co-authored-by: Daniel Bevenius <redacted>
* Address reviewer feedback: remove extra indentation around static xcframework creation.

* squash! Address reviewer feedback: remove extra indentation around static xcframework creation.

Fix whitespaces.

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Co-authored-by: Daniel Bevenius <redacted>