Fix for #1624 and #1623: Bootstrap_Nav_Walker::start_el() continued

[benlk]

Changes

As noted in #1623 (comment), cannot use object of type stdClass as array in largo/inc/nav-menus.php:87. This PR reverts to the pre-#1624 behavior of accessing the various aspects of the $args argument as object properties, not as array keys.

I'm not sure what caused #1623, in the end, and that's worrisome.

However, this patch unbreaks the error that #1624 introduced.

[benlk]

Testing

• Compare markup from this class before and after this commit has been applied. They should be identical.
• Compare markup from this commit and from v0.5.5.4. They should be identical.

[benlk]

Under PHP 7.3:

On a post:

• 0.5.5.4.txt
• 17caa1eadcc889b19af8047d6369428fce8e7823.txt — the commit before In Bootstrap_Walker_Nav_Menu::start_el(), stop referring to array keys as object properties, and set visibility of methods. #1624
• branch.txt from In Bootstrap_Walker_Nav_Menu::start_el(), stop referring to array keys as object properties, and set visibility of methods. #1624
• new-branch.txt from this PR

For the homepage:

• 0.5.5.4.txt
• 17caa1eadcc889b19af8047d6369428fce8e7823.txt
• new-branch.txt

Compared to last time (#1624):

• 100% fewer errors on the homepage
• arguments are object properties, not array keys.