Compile starts/ends with using str_starts_with and str_ends_with

[GromNaN]

Since we now require PHP 8.0 polyfill #3884, we can use str_starts_with and str_ends_with to compile starts with and ends with expressions.

Example with bootstrap_4_layout.html.twig line 6-7 (see deep diff):

    {%- set prepend = not (money_pattern starts with '{{') -%}
    {%- set append = not (money_pattern ends with '}}') -%}

// line 6
- $context["prepend"] =  !(is_string($__internal_compile_0 = (isset($context["money_pattern"]) || array_key_exists("money_pattern", $context) ? $context["money_pattern"] : (function () { throw new RuntimeError('Variable "money_pattern" does not exist.', 6, $this->source); })())) && is_string($__internal_compile_1 = "{{") && ('' === $__internal_compile_1 || 0 === strpos($__internal_compile_0, $__internal_compile_1)));
+ $context["prepend"] =  !(is_string($__internal_compile_0 = (isset($context["money_pattern"]) || array_key_exists("money_pattern", $context) ? $context["money_pattern"] : (function () { throw new RuntimeError('Variable "money_pattern" does not exist.', 6, $this->source); })())) && is_string($__internal_compile_1 = "{{") && str_starts_with($__internal_compile_0, $__internal_compile_1));
// line 7
- $context["append"] =  !(is_string($__internal_compile_2 = (isset($context["money_pattern"]) || array_key_exists("money_pattern", $context) ? $context["money_pattern"] : (function () { throw new RuntimeError('Variable "money_pattern" does not exist.', 7, $this->source); })())) && is_string($__internal_compile_3 = "}}") && ('' === $__internal_compile_3 || $__internal_compile_3 === substr($__internal_compile_2, -strlen($__internal_compile_3))));
+ $context["append"] =  !(is_string($__internal_compile_2 = (isset($context["money_pattern"]) || array_key_exists("money_pattern", $context) ? $context["money_pattern"] : (function () { throw new RuntimeError('Variable "money_pattern" does not exist.', 7, $this->source); })())) && is_string($__internal_compile_3 = "}}") && str_ends_with($__internal_compile_2, $__internal_compile_3));

[GromNaN]

An additional optimization could be to remove the is_string($right = <right>) when the right expression is a constant string. And using strict mode, it should throw an exception if it is a constant that is not a string.

[fabpot]

Thank you @GromNaN.