[Table] Always disable batch-rendering in headers

[cmslewis]

Changes proposed in this pull request:

• 🔄 CHANGED Table now always disables batch rendering for header cells.
  • Why? Because we kept seeing race conditions where we tried to sync quadrant row-header sizes before the final header cells finished rendering, leading to mismeasurements. The cost here is likely minimal, since header cells are less numerous than body cells and generally won't have tons of content in them (e.g. they won't have huge JSON blobs or detectTruncation logic).

[blueprint-bot]

Delete Batcher code

Preview: documentation | table
Coverage: core | datetime

[llorca]

Feels pretty good for column headers. Is it now also disabled for row headers? They don't particularly feel that much faster

[gscshoyru]

...well that's straightforward enough

[giladgray]

nice deletions

[cmslewis]

@llorca yep, it's disabled in the generic Header component, which both row and column headers use internally.