DocMeta: Access META binding through invokelatest

[topolarity]

Starting in Julia 1.12, global bindings have strict world-age semantics so this change is required to avoid the warning introduced by JuliaLang/julia#57133

Resolves #2621. This replaces #2622, which took things in the right direction but was missing a few required invokelatest

Close #2621, close #2622.

[topolarity]

I'm really not sure why this is causing:

PR #1634, issue #1655: Test Failed at /home/runner/work/Documenter.jl/Documenter.jl/test/utilities.jl:390
  Expression: (exs[1])[2] == "1 + 1\n# comment\n\n"
   Evaluated: "1 + 1\n" == "1 + 1\n# comment\n\n"

on nightly

[topolarity]

Ah, that's most likely an unrelated problem due to JuliaLang/julia#57280

[mortenpi]

Thank you @topolarity (and @lgoettgens) ! I was wondering about the isdefineds. This LGTM, and I will go ahead and merge this, and we'll see if we can sort of the rest of the CI failures..