Button Block: Allow custom width

[bhubbard]

What problem does this address?

Currently with the button block, I can choose several popular widths, 25%, 50%, 75%, 100%. However I want to create a pattern with 3 buttons together in a row, and need to provide a more specific pattern. Example of the pattern:

What is your proposed solution?

Keep the popular widths, but have an advanced option to provide a specifics widths, px, %, rem, etc.

[prasadkarmalkar]

I would like to work on this issue, I was thinking of using the FontSizePicker for choosing the size of button, So that we can use the custom widths like px, % and rem.
In current implementation the size is added via CSS class that are by default, So to make it dynamic I was thinking of removing the default CSS classes given and use direct style attribute inside the block for custom sizes.
Here are some of the screenshots

[mirka]

When I look at all the blocks that had this "25%, 50%, 75%, 100%" control, they have now mostly been standardized to use the DimensionTool (see for example #52223). Can we use that here, too?