Propagate SCOPE.compiles for nested functions in traits(compiles) blocks

[RazvanN7]

While trying to fix [1][2], I noticed that when a function's body is semantically analyzed the SCOPE.compiles field is always set to 0. Digging through what has caused this, I noticed that this was done to prevent traits(compiles) blocks from affecting the inferred attributes of the outer function. However, this has the side effect that functions that are nested in the traits(compiles) lose this information. This information is necessary for [2], which currently works around this issue by using one of the 4 different ways of checking if we are in a speculative scope, but should use SCOPE.compiles after this is merged. I suspect that this will also make it easy to get rid of the useless complexity added by [3].

[1] https://issues.dlang.org/show_bug.cgi?id=23650
[2] #14844
[3] #7897

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[dkorpel]

Thanks for untangling this mess