Tokenizer: apply tab replacement to heredoc/nowdoc opener

[jrfnl]

Description

You learn something new every day :wink:

While probably exceedingly rare to be found in actual codebases, the PHP tokenizer apparently allows for whitespace between the <<< and the heredoc/nowdoc identifier. See: https://3v4l.org/NUHZd

Both spaces as well as tabs are allowed. New lines are not allowed. Comments are also not allowed. See: https://3v4l.org/7PIEK

The PHPCS Tokenizer did not execute tab replacement on these tokens leading to unexpected 'content' and incorrect 'length' values in the File::$tokens array, which in turn could lead to incorrect sniff results and incorrect fixes.

This commit adds the T_START_HEREDOC/T_START_NOWDOC tokens to the array of tokens for which to do tab replacement to make them more consistent with the rest of PHPCS.

Includes unit tests safeguarding this change.

Suggested changelog entry

Tokenizer not applying tab replacement to heredoc/nowdoc openers

Related issues/external references

Ref: https://externals.io/message/124462#124518

Loosely related to: https://github.com/squizlabs/PHP_CodeSniffer/pull/3639 in which a similar change was made for heredoc/nowdoc closers (in the context of PHP 7.3+ flexible heredocs/nowdocs).

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)

[jrfnl]

Rebased without changes. Merging once the builds has passed.