Assert when subtracting stringpiece iterators

[s-perron]

When using the latest RE2, the windows debug builds give an assert.

effcee/effcee/check.cc

Line 121 in 77a53ba

input->remove_prefix(captured->end() - input->begin());

This subtraction with two iterators from different stringpieces gives an assert:

C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.36.32532\include\xstring(1086) : Assertion failed: cannot subtract incompatible string_view iterators

This is caused by the definition of the re2 StringPiece class being replaced with std::string_view.

Is there another way to do what we want to do in effcee?