refactor: rename vim.highlight => vim.hl

Problem:
- `vim.highlight` module does not follow `:help dev-name-common`, which
  documents the name for "highlight" as "hl".
- Shorter names are usually preferred.

Solution:
Rename `vim.highlight` to `vim.hl`.

This is not a breaking change until 2.0 (or maybe never).

runtime/doc/deprecated.txt

@@ -21,6 +21,7 @@ API
 
 LUA
 - vim.region()		Use |getregionpos()| instead.
+- *vim.highlight*	Renamed to |vim.hl|.
 
 DIAGNOSTICS
 - *vim.diagnostic.goto_next()*	Use |vim.diagnostic.jump()| with `{count=1, float=true}` instead.

runtime/doc/lsp.txt

@@ -464,7 +464,7 @@ Use |:Inspect| to view the highlights for a specific token. Use |:hi| or
     hi @lsp.mod.deprecated gui=strikethrough  " deprecated is crossed out
     hi @lsp.typemod.function.async guifg=Blue " async functions are blue
 <
-The value |vim.highlight.priorities|`.semantic_tokens` is the priority of the
+The value |vim.hl.priorities|`.semantic_tokens` is the priority of the
 `@lsp.type.*` highlights. The `@lsp.mod.*` and `@lsp.typemod.*` highlights
 have priorities one and two higher, respectively.
 
@@ -1780,8 +1780,8 @@ highlight_token({token}, {bufnr}, {client_id}, {hl_group}, {opts})
       • {hl_group}   (`string`) Highlight group name
       • {opts}       (`table?`) Optional parameters:
                      • {priority}? (`integer`, default:
-                       `vim.highlight.priorities.semantic_tokens + 3`)
-                       Priority for the applied extmark.
+                       `vim.hl.priorities.semantic_tokens + 3`) Priority for
+                       the applied extmark.
 
 start({bufnr}, {client_id}, {opts})          *vim.lsp.semantic_tokens.start()*
     Start the semantic token highlighting engine for the given buffer with the

runtime/doc/lua-guide.txt

@@ -552,7 +552,7 @@ This means that if your callback itself takes an (even optional) argument, you
 must wrap it in `function() end` to avoid an error:
 >lua
     vim.api.nvim_create_autocmd('TextYankPost', {
-      callback = function() vim.highlight.on_yank() end
+      callback = function() vim.hl.on_yank() end
     })
 <
 (Since unused arguments can be omitted in Lua function definitions, this is
@@ -576,7 +576,7 @@ Instead of using a pattern, you can create a buffer-local autocommand (see
 Similarly to mappings, you can (and should) add a description using `desc`:
 >lua
     vim.api.nvim_create_autocmd('TextYankPost', {
-      callback = function() vim.highlight.on_yank() end,
+      callback = function() vim.hl.on_yank() end,
       desc = "Briefly highlight yanked text"
     })
 <

runtime/doc/lua.txt

@@ -636,13 +636,13 @@ A subset of the `vim.*` API is available in threads. This includes:
 
 
 ==============================================================================
-VIM.HIGHLIGHT                                                  *vim.highlight*
+VIM.HL                                                                *vim.hl*
 
-vim.highlight.on_yank({opts})                        *vim.highlight.on_yank()*
+vim.hl.on_yank({opts})                                      *vim.hl.on_yank()*
     Highlight the yanked text during a |TextYankPost| event.
 
     Add the following to your `init.vim`: >vim
-        autocmd TextYankPost * silent! lua vim.highlight.on_yank {higroup='Visual', timeout=300}
+        autocmd TextYankPost * silent! lua vim.hl.on_yank {higroup='Visual', timeout=300}
 <
 
     Parameters: ~
@@ -655,9 +655,9 @@ vim.highlight.on_yank({opts})                        *vim.highlight.on_yank()*
                   true)
                 • event event structure (default vim.v.event)
                 • priority integer priority (default
-                  |vim.highlight.priorities|`.user`)
+                  |vim.hl.priorities|`.user`)
 
-vim.highlight.priorities                            *vim.highlight.priorities*
+vim.hl.priorities                                          *vim.hl.priorities*
     Table with default priorities used for highlighting:
     • `syntax`: `50`, used for standard syntax highlighting
     • `treesitter`: `100`, used for treesitter-based highlighting
@@ -666,8 +666,8 @@ vim.highlight.priorities                            *vim.highlight.priorities*
     • `user`: `200`, used for user-triggered highlights such as LSP document
       symbols or `on_yank` autocommands
 
-                                                       *vim.highlight.range()*
-vim.highlight.range({bufnr}, {ns}, {higroup}, {start}, {finish}, {opts})
+                                                              *vim.hl.range()*
+vim.hl.range({bufnr}, {ns}, {higroup}, {start}, {finish}, {opts})
     Apply highlight group to range of text.
 
     Parameters: ~
@@ -684,8 +684,7 @@ vim.highlight.range({bufnr}, {ns}, {higroup}, {start}, {finish}, {opts})
                    • {inclusive}? (`boolean`, default: `false`) Indicates
                      whether the range is end-inclusive
                    • {priority}? (`integer`, default:
-                     `vim.highlight.priorities.user`) Indicates priority of
-                     highlight
+                     `vim.hl.priorities.user`) Highlight priority
 
 
 ==============================================================================

runtime/doc/vim_diff.txt

@@ -249,7 +249,7 @@ backwards-compatibility cost. Some examples:
 
 Some features are built in that otherwise required external plugins:
 
-- Highlighting the yanked region, see |vim.highlight|.
+- Highlighting the yanked region, see |vim.hl|.
 
 ARCHITECTURE