Backpropagate global and attention layers together (#9335)

* Merged commit includes the following changes:
326369548  by Andre Araujo:

    Fix import issues.

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326159826  by Andre Araujo:

    Changed the implementation of the cosine weights from Keras layer to tf.Variable to manually control for L2 normalization.

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326139082  by Andre Araujo:

    Support local feature matching using ratio test.

    To allow for easily choosing which matching type to use, we rename a flag/argument and modify all related files to avoid breakages.

    Also include a small change when computing nearest neighbors for geometric matching, to parallelize computation, which saves a little bit of time during execution (argument "n_jobs=-1").

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326119848  by Andre Araujo:

    Option to measure DELG latency taking binarization into account.

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324316608  by Andre Araujo:

    DELG global features training.

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323693131  by Andre Araujo:

    PY3 conversion for delf public lib.

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321046157  by Andre Araujo:

    Purely Google refactor

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PiperOrigin-RevId: 326369548

* Added export of delg_model module.

* README update to explain training DELG global features head

* Added guidelines for DELF hyperparameter values

* Fixed typo

* Added mention about remaining training flags.

* Merged commit includes the following changes:
334723489  by Andre Araujo:

    Backpropagate global and attention layers together.

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334228310  by Andre Araujo:

    Enable scaling of local feature locations to the resized resolution.

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PiperOrigin-RevId: 334723489

Co-authored-by: Andre Araujo <andrearaujo@google.com>