Problem:
The magic globals `it`, `describe`, etc., are more trouble than they are
worth.
- Hooking into `after_each` requires `getfenv()` hacks.
- They confuse luals/emmylua, because the top-level `.luarc.json` isn't
merged with `test/.luarc.json` (apparently a luals limitation?)
- They totally defeat discoverability because the user just has to
"know" about the various magic symbols.
So they harm DX, which means they serve no purpose at all.
Solution:
- Expose the test API from `testutil`, so tests can call `t.it()`,
`t.describe()`, etc., in the conventional way.
- Drop `getfenv()` hacks.
- Drop the `setfenv()` injection in `load_chunk`.
- Drop `test/_meta.lua`.
Problem:
Can't expand treesitter-incremental-selection to the next and previous
sibling nodes.
Solution:
Pressing `]N` in visual mode will expand the selection to the next
sibling node, and `[N` will do the same with the previous node.
Problem:
`TSNode:id()` returns the underlying c pointer as a string, which may include
NUL bytes. In PUC Lua, `('%s'):format('\0a\0')` returns `''` and not `'\0a\0'`
(i.e. treats the string as a c-string (which terminates at the NUL byte)).
This resulted in two different nodes being able to have the same id.
Solution:
Use concatenation `..` instead of `string.format()`.
