Inline Formula Editor: with drag to reference cells

[luke-quadratic]

Creating an inline formula editor would make it possible to use the mouse and keyboard to reference nearby cells. This is very difficult to do with a multiline code editor.

We should by default, have the formula editor inline like traditional spreadsheets, with a way to switch to the multiline editor.

Scope:

• Inline formula editor
• Keyboard to select cells
• Mouse to select cells
• Ability to switch between inline and code editor for formulas
• Switch key bindings = does formulas / opens the code menu.

Expected spreadsheet behavior for dragging cells to replicate formulas e.g. SUM for multiple cells; should mimic universal
spreadsheet behavior

(ignore for Python, just do for Formulas)

[luke-quadratic]

This feature should also include this: #860

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