Border styles produced in inline styles could be more optimal

[pomek]

📝 Provide a description of the improvement

Consider the following examples.

Model	Invalid (current) view	Expected view	The "Why?"
<table borderStyle="solid">	<table style="border-bottom:solid;border-left:solid;border-right:solid;border-top:solid;">	<table style="border-style:solid;">	border-* requires all values (width, style, color) to proper display the element. If any is missing, the "initial" data will be applied which is wrong because it overrides the default styles (from the website).
<table borderStyle="solid" borderWidth="2px">	<table style="border-bottom:2px solid;border-left:2px solid;border-right:2px solid;border-top:2px solid;">	<table style="border-style:solid;border-width:2px;">	Same as above.
<table borderColor="#f00" borderStyle="solid" borderWidth="2px">	<table style="border-bottom:2px solid #f00;border-left:2px solid #f00;border-right:2px solid #f00;border-top:2px solid #f00;">	<table style="border:2px solid #f00;">	If all border definitions are the same, why couldn't we merge them into single property?

It is also possible to load different values than the editor accepts. E.g. when loading the table will the following styles:

/* Assuming that border-color defines the website. */
border-top-style: solid;
border-top-width: 2px;
border-right-style: solid;
border-right-width: 4px;
border-bottom-style: solid;
border-right-width: 6px;
border-left-style: solid;
border-left-width: 8px;

The editor should return:

/* border-style is merged into the single property. */
border-style: solid;
border-top-width: 2px;
border-right-width: 4px;
border-right-width: 6px;
border-left-width: 8px;