Introduce strict-text and posn-strict-text wrappers and monadUserState-strict-text

[alexbiehl]

This PR introduces the strict-text and posn-strict-text wrappers to allows working with Data.Text out of the box.

Implementation wise we could do a bit better by using Data.Text.Foreign.takeWord8 and avoiding the intermediate list of bytes in a codepoint but this will do for now.

[alexbiehl]

~Hm, tests do pass locally, not sure what's causing the issue.~

[andreasabel]

(As you already noticed) text is only a GHC-shipped package from 8.4 on, compare the release notes:

• https://downloads.haskell.org/~ghc/8.2.2/docs/html/users_guide/8.2.1-notes.html
• https://downloads.haskell.org/~ghc/8.4.2/docs/html/users_guide/8.4.1-notes.html#included-libraries

Adding a dependency like text might require to cabalize the testsuite first. (It's Makefile design is ancient, probably predating cabal.)

[alexbiehl]

@andreasabel It looks like to fully cabalize the test suite is a long term effort, how about I disable the text specific tests on old GHCs?

[andreasabel]

how about I disable the text specific tests on old GHCs?

Yes, that seems fair, especially since you add a new feature so it is less important to test it with old GHCs.

[alexbiehl]

Cool! Squash is fine.

[andreasabel]

I now tested this PR locally by porting one of my projects to the new posn-strict-text wrapper. Worked!

[andreasabel]

A new major version (3.4.0.0) looks more appropriate for a new feature, one can then have build-tool-depends: alex:alex >= 3.4 (rather than 3.3.1).