Move Dense and Dropout layers to separate files

[rickwierenga]

For details see: https://groups.google.com/a/tensorflow.org/forum/m/#!topic/swift/-I-P8wjhsTg

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[rickwierenga]

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[rickwierenga]

I just noticed (too late) that this PR also includes the precondition described here. Is this a problem?

[Shashi456]

@rickwierenga, it's ideal if we keep the splitting of core.swift into separate files and this precondition as separate PRs

[Shashi456]

No extra spaces at the end of files.

[saeta]

I think this LGTM, and can go in if there are no other concerns & it passes CI.

[saeta]

FWIW, although it's generally better to have one logical change per PR, given that this is just one statement, I think it's probably okay to leave in.

Note: this change would break users who relied upon probability outside the range acting as if it's clamped to the range. I think this is okay, however, as this likely indicates a bug. That said, if we wanted to, we could provide a convenience initializer that would do the clamping to 0...1 and then delegate to this initializer. (This could be done in a follow-on PR.)

[rickwierenga]

FWIW, although it's generally better to have one logical change per PR, given that this is just one statement, I think it's probably okay to leave in.

You are absolutely right. I forgot to exclude it in the commit--will look more closely in the future.

Note: this change would break users who relied upon probability outside the range acting as if it's clamped to the range. I think this is okay, however, as this likely indicates a bug. That said, if we wanted to, we could provide a convenience initializer that would do the clamping to 0...1 and then delegate to this initializer. (This could be done in a follow-on PR.)

The convenience initializer ia a great idea. I think it should show some kind of message though indicating the input value will be clamped. Should this be a permanent or temporary initializer (with deprecation warning)?

[rickwierenga]

Just fixed the ordering issue. I will leave the changes in Dropout.swift for the next PR.

[dan-zheng]

Thanks @rickwierenga!