[sdl2-ttf,tgui,sfml] Update sdl2-ttf to 2.20.0, revise dependencies import and export

[dg0yt]

Reprise of #25803 (@Thomas1664), #25713 (@FrankXie05). They made the major work.

• What does your PR fix?

  Fixes [sdl2-ttf] update to 2.20.0 #25661.
  Modernizes tgui, and updates import and export of dependencies.
  Fixes and updates import and export of dependencies in port sfml, in particular OpenGL, needed for building tgui[tool]:x64-linux.

• Which triplets are supported/not supported? Have you updated the CI baseline?

  unchanged, no

• Does your PR follow the maintainer guide?

  yes

• If you have added/updated a port: Have you run ./vcpkg x-add-version --all and committed the result?

  yes

[dg0yt]

• SFML is the default backend in TGUI. Using the SDL backend requires user to explicitly add
  #include <TGUI/Backends/SDL.hpp>.
• The TGUI pc file isn't installed for all platforms, the given lib name doesn't match the actual file name for most configurations, and dependencies are completely missing.

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When making any changes to a library, the version or port-version in vcpkg.json or CONTROL must be modified.

error: checked-in files for milerius-sfml-imgui have changed but the version was not updated
version: 1.1#5
old SHA: 9688f88e4f66e2c8ef9f40b45218ffb88d86e061
new SHA: ab049da96ffce2ca97cf13a61b4f2a657cb2d478
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***No files were updated***

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[github-actions]

You have modified or added at least one vcpkg.json where you should check the license field.

If you feel able to do so, please consider adding a "license" field to the following files:

• ports/milerius-sfml-imgui/vcpkg.json

Valid values for the license field can be found in the documentation

[dg0yt]

@FrankXie05 Then please run with CMAKE_FIND_DEBUG_MODE enabled. I assume it is available, but not accepted due to some missing dependency.

[BillyONeal]

Thanks for the updates! (And also @Thomas1664 and @FrankXie05 )