Remove dead code based on evaluated constant expression

[staabm]

Before

if (time() > strtotime('30 Nov 2018')) {
  // do something1
} else if (time() > strtotime('30 Nov 2019')) {
  // do something2
} else {
  // do something3
}

After running with min php version = 7.3

  // do something3

Inspired by https://github.com/redaxo/redaxo/blob/46d0ace6cd1ca0d40fa233abd637bea53c694daa/redaxo/src/core/pages/setup.php#L147

Phpstan e.g. does similar things with printf() in case the format pattern can be constructed at parse time, some validation runs
I guess its implemented in https://github.com/phpstan/phpstan-src/blob/699c420f8193da66927e54494a0afa0c323c6458/src/Rules/Functions/PrintfParametersRule.php

https://github.com/phpstan/phpstan-src/blob/699c420f8193da66927e54494a0afa0c323c6458/src/Type/Php/SprintfFunctionDynamicReturnTypeExtension.php

https://github.com/phpstan/phpstan-src/blob/699c420f8193da66927e54494a0afa0c323c6458/src/Type/Php/StrtotimeFunctionReturnTypeExtension.php

Related phpstan/phpstan#2812

[TomasVotruba]

I'm 👍 for this.
Feel free to send PR with such feature.