The II operator takes a range and returns a single cell that is in the same column or the same row
as the present cell.
This is needed for backwards compatibility with old Excel models and as a first step towards dynamic arrays.
In the past Excel would evaluate `=A1:A10` in cell `C3` as `A3`, but today in results in an array containing all
values in the range. To be compatible with old workbooks Excel inserts the II operator
on those cases.
So this PR performs an static analysis on all formulas inserting on import automatically the II operator
where necessary. This we call the _automatic implicit operator_. When exporting to Excel the operator is striped away.
You can also manually use the II. For instance `=SUM(@A1:A10)` in cell `C3`.
This was not possible before and such a formula would break backwards compatibility with Excel. To Excel that "non automatic"
form of the II is exported as `_xlfn.SINGLE()`.
Th static analysis has to be done for all arithmetic operations and all functions.
This is a bit of a daunting task and it is not done fully in this PR. We also need to implement arrays and dynamic arrays.
My believe is that once the core operations have been implemented we can go formula by formula writing proper tests and documentation.
After this PR formulas like `=A1:A10` for instance will return `#N/IMPL!` instead of performing the implicit intersection
What are we trying to achieve ?
++ Currently all the major public set functions is panic prone and does not handle and return error. This PR tries to address to all those functions.
What major errors that could happen in these functions ?
++ All the functions which are being made as error safe is being tested against invalid sheet, row and column values, which could given by user
What are the list of functions whose return type has been altered ?
**base/src/model.rs**
1. update_cell_with_text
2. update_cell_with_bool
3. update_cell_with_number
4. set_user_input
5. get_cell_style_index
6. get_style_for_cell
7. set_cell_with_string
++> New functions being added
1. set_cell_with_boolean
2. set_cell_with_number
**base/src/styles.rs**
1. get_style_with_quote_prefix
3. get_style_with_format
4. get_style_without_quote_prefix
5. get_style
**base/src/worksheet.rs**
1. update_cell
2. set_cell_style
3. set_cell_with_formula
4. set_cell_with_number
6. set_cell_with_string
8. set_cell_with_boolean
9. set_cell_with_error
10. cell_clear_contents
11. cell_clear_contents_with_style
++> Above is the comprehensive list of all functions being ( most are public, some are private ) altered for better error handling. As a side effect of changing function signature, there are many changes being done to other functions ( mostly adding "?" to enable to error propagation further )
