bitbake: runqueue: Reimplement recrdepends so it works more correctly

Currently, recrdepends is extremely greedy. For example:

do_foo[rdepends] = "somedep:sometask"
addtask foo

which adds foo with *no* dependencies, will suddenly start appearing
as a dependency in every task which uses recrdepends. So far this has
been mildy annoying but we now have use cases where this makes no sense
at all.

This reworks the recrdepends code to avoid this problem. To do this we
can no longer collapse things into lists just based on file ID. The problem
is this code is extremely performance sensitive. The "preparing runqueue"
phase spends a lot of time in these recursive dependency calculations so any
change here could negatively impact the user experience.

As such, this code has been carefully tested on convoluted dependency trees
with operations like "time bitbake world -g". The net result of this change
and the preceeding changes combined is a net speed up of these operations in
all cases measured.

Tests were made comparing "bitbake world -g" task-depends.dot before and after
this patch. There *are* differences for example -nativesdk do_build dependencies
on -native recipes are no longer present. All removed dependencies appear to
be sensible improvements to the system. The "rdepends" cross contamination
issue above is also fixed.

(Bitbake rev: 82d73423c57569b984ee0ae3d93e3c3bd5dc5216)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

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