Block Library: Table: Inserting new column with header present lacks cells

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Describe the bug

If a Table block includes a header or footer, proceeding to add a new column will not insert cells for that column.

To reproduce

Steps to reproduce the behavior:

1. Navigate to Posts > Add New
2. Insert a Table block
3. Choose Column/Row Count and press "Create Table" (specific values do not matter)
4. Toggle "Header section" in the Block Inspector "Table Settings" sidebar
5. Select a cell in the table
6. From the "Edit Table" Block Toolbar menu, select "Add Column Before" or "Add Column After"
7. Note that the last column does not include cells under its header

Similar issue exists for "Footer section" as well.

Expected behavior

The table should have a complete set of cells corresponding to the number of rows/columns.

Desktop (please complete the following information):

• OS: macOS Mojave 10.14.5 (18F132)
• Browser: Chrome Version 74.0.3729.169 (Official Build) (64-bit)