[TASK] Remove thecodingmachine/safe dependency (part 1)

[SjorsO]

As discussed here: #1484 (comment)

preg_match can return false if:

• The pattern is invalid
• the u flag is used and the subject or pattern aren't valid UTF-8
• Backtrack/recursion limits are hit

This preg_match can't fail because:

• The pattern is always valid ($match is always a fixed value)
• There is no u flag
• There is no backtracking or recursion

[coveralls]

coverage: 72.604% (+0.03%) from 72.579% — SjorsO:drop-dependency-part-1 into MyIntervals:main

[JakeQZ]

This preg_match can't fail because:

• There is no backtracking or recursion

Actually there is backtracking, or at least the storage of backtracking information. The engine is simple and does not know what it might be matching next. So when matching the optional vendor-prefix, it needs to be able to rewind in case the following part will match without it but not with. We can see that's not possible, but it can't. So it will build up a rewind stack. If presented with something like -veryverylongvendorprefix-translate (shortened for readability), it could bail.

Use of the possessive quantifier will mitigate this. I think that's beyond the scope of these PRs, so have added #1614.

The library as it is should bail out somehow reasonably in such unrealistic situations, as well as it did before the introduction of 'Safe', and at least there is now an assert().