[pgAdmin4][PATCH] Improvements to Query Results Grid User Experience

Hi Hackers!

Attached are the updates to the query results grid, broken up into four
patches.

Description of the Completed Functionality After Applying All Four Patches
Currently the designed behavior is somewhere between excel like behavior
and not. As such we can describe the behavior as follows:

- Select columns by clicking on the header
- Select rows by clicking on the row header (column 0)
- You can drag and select with the mouse
- You can select all with ctrl+a or by clicking the upper left cell
- You can copy with ctrl+c or with the copy icon
- you can increase or decrease the size of the selected area with
shift+arrow
- shift+arrow understands directionality, e.g. drag select from left to
right differs from drag select from right to left
- Clicking anywhere outside of the selected area deselects the area and
reselects the new cell(s) clicked on

Current potentially awkward but intentional functionality

- When you select multiple columns/rows by clicking on the header, then
press shift+arrow all but the last selected columns/rows are deselected

Includes fixes for:
RM Bug #2348 - On resize of first/any column in "Query Tool/View Data" will
select/deselect all the rows/columns.
RM Bug #2344 - ctrl+v and ctrl+c need to work

*Detailed Description of Each Patch*

*0001-Improves-user-s-ability-to-select-cells-in-query-res.patch* -

- user can select columns

- user can modify column or row selection with shift+arrow

- user can select entire grid with ctrl+A or cmd+A

- user can copy from grid using keyboard shortcuts

*0002-Drag-and-select-from-data-grid.patch* -

*0003-Removes-checkboxes-from-the-grid.patch* -

- Changes header color to grey

*0004-Introduces-XCellSelectionModel.patch* -

- header styles depend on the selection

- show the correct row/column when scrolling up or left

- fixes drag and drop when drop is done outside the grid

Thanks,

Matt & Shruti