Columns: Width recalculation does not work correctly when number of columns is increased by more than 2 at once

[t-hamano]

Description

When the number of columns is changed in a Columns block, if the columns all have percentage widths, the sum of the widths of each column is recalculated to be exactly 100%. However, when the number of columns is increased by 2 or more, it doesn't seem to be completely 100%.

So it looks like the current logic only takes into account the case where the number of columns increases by 1.

For example, assume that each of the four columns has the following widths:

| 20% | 30% | 30% | 20% |

✅ Correct: When the number of columns increases from 4 to 5

| 16% | 24% | 24% | 16% | 20% |

Total: 100%

✅ Correct: When the number of columns is reduced from 4 to 3

| 25% | 37.5% | 37.5% |

Total: 100%

✅ Correct: When the number of columns is reduced from 4 to 2

| 40% | 60% |

Total: 100%

❌ Wrong: When the number of columns increases from 4 to 6

| 16.67% | 25% | 25% | 16.67% | 16.67% | 16.67% |

Total: 116.68%

Step-by-step reproduction instructions

• Insert a Columns block.
• Set percentage widths for all columns so that they add up to 100%.
• Select the Columns block and increase the number of columns by two or more without using the slider.
• Calculate the total percentage width of each Column block.

Screenshots, screen recording, code snippet

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Environment info

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Please confirm that you have searched existing issues in the repo.

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Please confirm that you have tested with all plugins deactivated except Gutenberg.

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