Specifically, functions that are run in the context of the test runner
are put in module `test/testutil.lua` while the functions that are run
in the context of the test session are put in
`test/functional/testnvim.lua`.
Closes https://github.com/neovim/neovim/issues/27004.
This is the first PR featuring a conversion of an upstream vim9script file
into a Lua file.
The generated file can be found in `runtime/autoload/ccomplete.vim` in
the vim repository. Below is a limited history of the changes of that file
at the time of conversion.
```
❯ git log --format=oneline runtime/autoload/ccomplete.vim
c4573eb12dba6a062af28ee0b8938d1521934ce4 Update runtime files
a4d131d11052cafcc5baad2273ef48e0dd4d09c5 Update runtime files
4466ad6baa22485abb1147aca3340cced4778a66 Update runtime files
d1caa941d876181aae0ebebc6ea954045bf0da24 Update runtime files
20aac6c1126988339611576d425965a25a777658 Update runtime files.
30b658179962cc3c9f0a98f071b36b09a36c2b94 Updated runtime files.
b6b046b281fac168a78b3eafdea9274bef06882f Updated runtime files.
00a927d62b68a3523cb1c4f9aa3f7683345c8182 Updated runtime files.
8c8de839325eda0bed68917d18179d2003b344d1 (tag: v7.2a) updated for version 7.2a
...
```
The file runtime/lua/_vim9script.lua only needs to be updated when vim9jit is updated
(for any bug fixes or new features, like implementing class and interface, the latest in vim9script).
Further PRs will improve the DX of generated the converted lua and
tracking which files in the neovim's code base have been generated.
