LibGfx/TIFF: Support samples with a floating point value

[LucasChollet]

The test cases were generated using this Python code (no extratags were
given for float32_no_tags):

import tifffile
import numpy as np
image = np.array(
                [[[0, 0, 0], [255, 0, 0]],
                [[0, 127.5, 127.5], [255, 255, 255]]]
            ).astype(np.float32)
tifffile.imwrite('float32.tiff', image / 255, extratags=[
        (340, 11, 3, [0, 0, 0], True),
        (341, 11, 3, [1, 1, 1], True)])

[stale]

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[nico]

Does anything in the wild use this? Do the uses set the SMin / SMax tags?

[stale]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed in 7 days if no further activity occurs. Thank you for your contributions!