BIDI: Bidi buttons should be selected in toolbar to reflect the current direction

[Damian]

There are a number of cases where it is difficult for a user to determine if the currently selected block has dir="RTL" or dir="LTR". E.g. we could have a paragraph that has dir="RTL" but aligned to the left.

To make it clear to a user which language direction is active, the toolbar buttons should select the relevant style.

1. When a block element has dir="LTR" or dir="RTL" the matching button in the toolbar should be selected.
2. When there is no explicit direction set on the block element, the toolbar button should show the currently active document level direction. E.g. if the document is LTR and the current paragraph does not have a dir attribute set, the LTR button in the toolbar should be selected. This is similar to the default behavior of the paragraph alignment buttons.

[Sa'ar Zac Elias]

Using getComputedStyle to calculate the current direction of the element.

[Sa'ar Zac Elias]

Fixed with [5729].