Reinstate traversal as "method of last resort" to find WordPress

[christianwach]

Overview

Follows on from #15919 to reinstate directory traversal as "method of last resort" to find WordPress location. Although the code in the previous commit should work most of the time, I'm reluctant to see the fallback code removed at this stage, even though there are issues with it.

Before

Fallback code removed.

After

Fallback code reinstated. I have rejigged the method so that the flow of logic is clearer.

Comments

Ultimately it would be good to be able to remove the fallback code, but I would like it to remain until all the directory traversal code can be conclusively and comprehensively removed.

[civibot]

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[seamuslee001]

I'm going to add merge on pass to this, makes sense to me

[christianwach]

@seamuslee001 Thanks!