PHP 7.0 makes many error conditions throw instances of the new Error class
which does not extend the known Exception.
The Throwable interface provides a concise and type-safe way of handling
either, e.g. for logging purposes, but HHVM did not support it, requiring
tedious fallback checks.
This commit replaces occurrences of Exception in code paths equally
covered by Throwable, like Exception|Throwable parameter and return types
(also nullable), instanceof guards, duplicated `catch` blocks, as well as
related comments and documentation blocks, with the exception of $previous
parameter descriptions consistent with the manual at
https://www.php.net/manual/en/exception.construct.php
Proper type declarations have been added or reinstated where possible.
Change-Id: I5d3920d3cc66936a350314e2f19c4f6faeffd7c0
1b3bc281ac