build: enable lintlua for test/ dir

Problem:
Not all Lua code is checked by stylua. Automating code-style is an
important mechanism for reducing time spent on accidental
(non-essential) complexity.

Solution:
- Enable stylua for entire `test/` directory.
- Exclude these high-churn files until this issue is resolved: JohnnyMorganz/StyLua#829
  ```
  test/functional/ui/decorations_spec.lua  | 3560 ++++++++++++++++++++++++++++++++++++----------------
  test/functional/ui/float_spec.lua        | 5826 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-------------------------
  test/functional/ui/multigrid_spec.lua    | 1349 ++++++++++++++------
  ```
- Make surgical changes to these files (or add `stylua: ignore` in some
  small scopes) to improve the result:
  ```
  test/functional/vimscript/msgpack_functions_spec.lua | 1414 +++++++++++++++------
  test/functional/api/buffer_spec.lua                  | 1389 +++++++++++----------
  test/functional/api/vim_spec.lua                     | 2740 +++++++++++++++++++++++-----------------
  ```
- These "high churn" files are NOT excluded because the changes are
  largely an improvement:
  ```
  test/functional/plugin/lsp_spec.lua      | 2198 ++++++++++++++++++---------------
  test/functional/plugin/shada_spec.lua    | 4078 +++++++++++++++++++++++++++++++++++-------------------------
  test/functional/ui/cmdline_spec.lua      | 1199 +++++++++++-------
  test/functional/ui/popupmenu_spec.lua    | 1267 +++++++++++--------
  test/functional/ui/messages_spec.lua     | 1643 +++++++++++++++---------
  ```
- TODO: how to check "all directories"? With `GLOB_DIRS *` and `/.deps/` (or
  `.deps/`) in `.styluaignore`, Lua code in `.deps/` is still checked...

.styluaignore

@@ -1,9 +1,9 @@
-/build
+/build/
+/.deps/
 /runtime/lua/coxpcall.lua
 /runtime/lua/vim/_meta
 /runtime/lua/vim/re.lua
 
-/test/functional
 /test/functional/fixtures/lua/syntax_error.lua
 /test/functional/legacy/030_fileformats_spec.lua
 /test/functional/legacy/044_099_regexp_multibyte_magic_spec.lua

CMakeLists.txt

@@ -226,16 +226,16 @@ add_glob_target(
   FLAGS -ll ${PROJECT_SOURCE_DIR}/test/lua_runner.lua ${CMAKE_BINARY_DIR}/usr luacheck -q
   GLOB_DIRS runtime/ scripts/ src/ test/
   GLOB_PAT *.lua
-  TOUCH_STRATEGY SINGLE)
+  TOUCH_STRATEGY PER_DIR)
 add_dependencies(lintlua-luacheck lua-dev-deps)
 
 add_glob_target(
   TARGET lintlua-stylua
   COMMAND ${STYLUA_PRG}
   FLAGS --color=always --check --respect-ignores
-  GLOB_DIRS runtime/ scripts/ src/ test/unit/
+  GLOB_DIRS runtime/ scripts/ src/ test/
   GLOB_PAT *.lua
-  TOUCH_STRATEGY SINGLE)
+  TOUCH_STRATEGY PER_DIR)
 
 add_custom_target(lintlua)
 add_dependencies(lintlua lintlua-luacheck lintlua-stylua)
@@ -246,7 +246,7 @@ add_glob_target(
   FLAGS -x -a
   GLOB_DIRS scripts
   GLOB_PAT *.sh
-  TOUCH_STRATEGY SINGLE)
+  TOUCH_STRATEGY PER_DIR)
 
 add_custom_target(lintcommit
   COMMAND $<TARGET_FILE:nvim> -u NONE -l ${PROJECT_SOURCE_DIR}/scripts/lintcommit.lua main)
@@ -260,8 +260,9 @@ add_glob_target(
   TARGET formatlua
   COMMAND ${STYLUA_PRG}
   FLAGS --respect-ignores
-  GLOB_DIRS runtime/ scripts/ src/ test/unit/
-  GLOB_PAT *.lua)
+  GLOB_DIRS runtime/ scripts/ src/ test/
+  GLOB_PAT *.lua
+  TOUCH_STRATEGY PER_DIR)
 
 add_custom_target(format)
 add_dependencies(format formatc formatlua)