Lazily compute outputs

[davidmorgan]

For #3811.

"outputs" are used at the start of the build to know what to invalidate/remove when updating the graph. Since they're not used during the build, they can be computed in one go instead of incrementally. It's not clear if there is a benefit to serializing them--stop doing that for now.

Benchmarks improve quite a bit due to no longer doing many repeated copies of the immutable "outputs" sets, and the JSON size is about halved.

before this PR
json_serializable
shape,libraries,clean/ms,no changes/ms,incremental/ms,json/KiB
loop,1,21805,3912,5216,454
loop,100,24872,4058,7354,5002
loop,250,27289,4901,11688,27067
loop,500,41936,7753,16928,104465
loop,750,76779,12352,23427,232645
loop,1000,133677,18266,37324,419464
forwards,1,21847,3851,5081,455
forwards,100,24577,3687,7520,3169
forwards,250,28194,4798,10244,15451
forwards,500,34165,5963,16175,57796
forwards,750,47009,8607,22132,127484
forwards,1000,70189,10267,26040,228472
backwards,1,22138,3970,5189,455
backwards,100,24881,4113,7513,3213
backwards,250,28388,4596,11579,15708
backwards,500,34640,5917,17745,58798
backwards,750,51449,8806,25058,129720
backwards,1000,75859,12535,32259,232430

with this PR
json_serializable
shape,libraries,clean/ms,no changes/ms,incremental/ms,json/KiB
loop,1,23492,3887,5292,417
loop,100,23786,3900,6928,2564
loop,250,27987,4494,9667,12674
loop,500,32715,5789,16602,47884
loop,750,37391,8292,22735,106042
loop,1000,43723,11432,30665,191073
forwards,1,22246,3762,5264,417
forwards,100,24092,3960,7265,1741
forwards,250,27831,4231,9800,7467
forwards,500,29865,5024,14991,26973
forwards,750,36458,6234,20061,58929
forwards,1000,39756,8070,28756,105307
backwards,1,22162,3845,5364,417
backwards,100,24036,4054,7900,1762
backwards,250,27503,4349,10938,7594
backwards,500,31306,5024,15695,27471
backwards,750,37975,6045,22651,60042
backwards,1000,43777,8021,27442,107280

[github-actions]

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[davidmorgan]

The CI issue is due to _macros package being removed in the latest dev SDK, unrelated to this change: kicked off a separate discussion for that.