Auto merge of #76256 - tgnottingham:issue-74890, r=nikomatsakis

incr-comp: hash and serialize span end line/column

Hash both the length and the end location (line/column) of a span. If we
hash only the length, for example, then two otherwise equal spans with
different end locations will have the same hash. This can cause a
problem during incremental compilation wherein a previous result for a
query that depends on the end location of a span will be incorrectly
reused when the end location of the span it depends on has changed. A
similar analysis applies if some query depends specifically on the
length of the span, but we only hash the end location. So hash both.

Fix #46744, fix #59954, fix #63161, fix #73640, fix #73967, fix #74890, fix #75900

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See #74890 for a more in-depth analysis.

I haven't thought about what other problems this root cause could be responsible for. Please let me know if anything springs to mind. I believe the issue has existed since the inception of incremental compilation.

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