https://github.com/tensorflow/tflite-micro makes use of flatbuffers with
a variety of DSP toolchains.
Without the change from this PR, we can get a double-promotion warning
with some of these DSP toolchains:
```
flatbuffers/include/flatbuffers/util.h:104:11: error: implicit conversion increases floating-point precision: 'std::numeric_limits<float>::_Ty' (aka 'float') to 'double' [-Werror,-Wdouble-promotion]
T eps = std::numeric_limits<float>::epsilon();
~~~ ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```
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