Update 're2' to 2023.09.01

[hjmallon]

• I've followed this guide
  step by step carefully. [Yes]

[rbsheth]

Can you check on the CI runs?

[hjmallon]

Useful spot from the CI, re2 has introduced an abseil dependancy. I guess it must be picking one up from my local env automatically. I will close this PR.

[rbsheth]

@hjmallon Thanks for your contributions! Perhaps we can introduce the abseil dependency through Hunter and update re2?

[hjmallon]

Yeah I guess it would need a fork of re2? Unless there are some cleverer forkless Hunter things possible now?

[NeroBurner]

Wanted to fork it for you, but there already is one, probably old, but exists already: https://github.com/cpp-pm/re2/

[hjmallon]

Thanks, to be honest I'm in no great need of new re2 (we only use it inside grpc) so I'm not going to get to this soon.

[NeroBurner]

latest upstream tag now also available as https://github.com/cpp-pm/re2/releases/tag/2023-09-01

if you get around to it. Hunterizing should be easy as the project already creates the re-config.cmake files itself. So only HunterGate and hunter_add_package() should be needed