Infinite recursion when every pipe in a bracketed token is inside quotes

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Problem/Motivation

Since #3491615 (2.3.3 and 3.0.0-beta1), text like [widget:name attr="a|b"] hangs the request. The quote-aware split returns a single part, equal to the whole match. It looks like a token, so TokenOrTokensPreAlter::tokensPreAlter() calls the token service on the same text, which fires hook_tokens_pre_alter() again, without end.

We hit it with shortcodes in node bodies. Article pages ran for 60 seconds and returned 503. 2.3.2 is not affected.

Steps to reproduce

\Drupal::token()->replace('[widget:x attr="a|b"]');

On 2.3.3 and 3.0.0-beta1 this runs until memory is exhausted. On 2.3.2 it returns the text unchanged.

Proposed resolution

Skip the match when the split gives fewer than two parts. MR with a kernel test follows.