missing "is always false/true" errors on class_exists, method_exists, .. #14683

Feature request

we are missing errors like

'Call to function class_exists() with 'CheckTypeFunctionCall\\_Interface' will always evaluate to false.'

see comments in https://phpstan.org/r/d8f84ae4-ff8a-4235-861f-52bb165dbfbc

a possible fix should incorporate ondrejs feedback