feat(react-table): add autoFitColumnsStrategy so DataGrid can auto-fit and resize columns together

[AKnassa]

Previous Behavior

DataGrid columns are only evenly spaced when column resizing is turned off. As soon as resizableColumns is enabled, auto-fit grows each column to its ideal width and gives all of the leftover container space to the last column — four default columns in a 1000px container render as 150 / 150 / 150 / 486 instead of 250 / 250 / 250 / 250. The last column is also rendered without a resize handle, so the one column that ballooned is the one column the user cannot drag back. There is no workaround.

New Behavior

A new opt-in option shares the leftover space equally instead:

<DataGrid
  resizableColumns
  resizableColumnsOptions={{ autoFitColumnsStrategy: 'even' }}
/>

• 'even': every column gets its ideal width plus an equal share of the remaining space — the same equally-spaced layout the grid has when resizing is off, while every column (including the last) stays resizable.
• A column the user resizes keeps exactly the width they chose; the other columns share the rest. When the container is too small, unresized columns shrink toward their minimum first, and resized columns only give up what the others cannot absorb.
• Once every column has been deliberately sized, the columns simply share the container again so no dead space appears after the last column.
• 'last-column' (default): behavior is completely unchanged — no existing test, snapshot, or story was re-baselined, and the default code path was verified byte-identical against the previous implementation across mixed drag/squash sequences.

The new Resizable Columns - Even container auto-fit story demonstrates the behavior using default columns (no columnSizingOptions), which is exactly the reporter's scenario.

A decision for maintainers: the issue is really about the default — reporters expect auto-fit + resize to keep equal spacing out of the box. This PR ships the fix as opt-in to stay strictly non-breaking, but we believe 'even' is a strong candidate to become the default in a future major/behavioral release. Happy to follow up either way.

Noted while working here, intentionally left out of scope: columnDefinitionsToState resets the first over-ideal column where it means the previously-stretched last one (columnResizeUtils.ts, currently masked by an invariant), and TableColumnSizingOptions declares a per-column autoFitColumns that no code reads. Can file separate issues for both.

Related Issue(s)

• Fixes [Bug]: DataGrid doesn't support default auto-fit and resize simultaneously #35923

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• Changes covered by tests (29 new tests: distribution math, min-width water-fill, resized-column pinning, container/column/options updates, keyboard-resize aria, single-column edge, SSR zero-width container)
• yarn change change file included (minor)
• API report regenerated (one added line)
• 521/521 tests, lint, type-check all passing locally

[AKnassa]

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