cherrypick-1.1: distsql: pre-reserve memory needed to mark rows in HashJoiner build phase

[asubiotto]

A situation was uncovered by #18600, where the HashJoiner would run out
of memory in the probe phase. This was because we had made an assumption
that we wouldn't hit a memory limit if the buffer phase filled up at
most 2/3 of the limit with both streams , since the marking
infrastructure would take up only a fraction of 1/3 (the chosen stream).

This assumption failed to take into account other limits shared with
other processors. This change pre-reserves the memory needed for the
probe phase in the build phase so that we can keep a single point in the
code where we fall back to disk while not relying on any limit
assumptions.

[cockroach-teamcity]

This change is 

[cockroach-teamcity]

This change is 

[andreimatei]

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[andreimatei]

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Review status: 0 of 3 files reviewed at latest revision, all discussions resolved, all commit checks successful.

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Comments from Reviewable