Fix UnicodeConversionError

[adriankumpf]

This fixes a UnicodeConversionError that gets raised by String.to_charlist/1 if Infer.Text.html? or Infer.Text.xml? receive a binary that is not UTF-8 encoded.

iex> String.to_charlist <<0xFF>>
** (UnicodeConversionError) invalid encoding starting at <<255>>
    (elixir 1.13.3) lib/string.ex:2407: String.to_charlist/1

iex> :binary.bin_to_list <<0xFF>>
[255]

I also added a bunch of Infer.Matchers tests for unexpected inputs, which increases the time to run the whole test suite a bit, mostly due to the size of some test files.

[daskycodes]

Thanks a bunch for the PR! 🚀

I will look into smaller test files as an improvement for getting the test suite even to better speeds!