Consider use of libjpeg-turbo extension framework for control over encoder settings

[lovell]

Hello, thanks for creating jpegli and many of the JPEG-XL features it descends from. This suggestion was originally discussed at lovell/sharp#4018 (comment) and I'm opening an issue here on the recommendation of lovell/sharp#4018 (comment)

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The libjpeg-turbo approved (and mozjpeg implemented) method of configuring a JPEG encoder whilst maintaining ABI compatibility is to use its extension framework.

This is provided via a series of functions such as jpeg_c_bool_param_supported and jpeg_c_set_bool_param (with similar functions for integer, float etc. types). These were added to mozjpeg via mozilla/mozjpeg@db2986c

As well as fine-grained control over specific encoder features, there is also a simpler JINT_COMPRESS_PROFILE setting that provides a single switch between "use all features" JCP_MAX_COMPRESSION and "do nothing, behave like libjpeg" JCP_FASTEST. This was added to mozjpeg via mozilla/mozjpeg@3e2cf69

For reference, the complete set of features mozjpeg exposes via the extension framework can be seen at https://github.com/mozilla/mozjpeg/blob/6c9f0897afa1c2738d7222a0a9ab49e8b536a267/jpeglib.h#L277-L314