text_join argument precedence bug in PHP

[bkisdi]

Problem statement

The text_join block uses incorrect argument precedence in PHP code generation.

Steps to Reproduce

Toggle true to false at the next run.

Actual Behavior

It produces 'T' or 'FX', based on the test value.

Expected Behavior

Return 'TX' or 'FX' respectively.

Additional Information

if (block.itemCount_ == 2), it uses Blockly.PHP.ORDER_NONE for its arguments instead of something smaller.
And should return [code, Blockly.PHP.ORDER_STRING_CONCAT] (which level is actually never used in the code base) instead of ORDER_ADDITION.