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/lua/vim/lsp/handlers.lua

@@ -437,7 +437,7 @@ function M.signature_help(_, result, ctx, config)
   local fbuf, fwin = util.open_floating_preview(lines, 'markdown', config)
   -- Highlight the active parameter.
   if hl then
-    vim.highlight.range(
+    vim.hl.range(
       fbuf,
       sig_help_ns,
       'LspSignatureActiveParameter',

runtime/lua/vim/lsp/semantic_tokens.lua

@@ -443,7 +443,7 @@ function STHighlighter:on_win(topline, botline)
         vim.api.nvim_buf_set_extmark(self.bufnr, state.namespace, token.line, token.start_col, {
           hl_group = hl_group,
           end_col = token.end_col,
-          priority = vim.highlight.priorities.semantic_tokens + delta,
+          priority = vim.hl.priorities.semantic_tokens + delta,
           strict = false,
         })
       end
@@ -723,7 +723,7 @@ end
 --- @inlinedoc
 ---
 --- Priority for the applied extmark.
---- (Default: `vim.highlight.priorities.semantic_tokens + 3`)
+--- (Default: `vim.hl.priorities.semantic_tokens + 3`)
 --- @field priority? integer
 
 --- Highlight a semantic token.
@@ -752,7 +752,7 @@ function M.highlight_token(token, bufnr, client_id, hl_group, opts)
   end
 
   opts = opts or {}
-  local priority = opts.priority or vim.highlight.priorities.semantic_tokens + 3
+  local priority = opts.priority or vim.hl.priorities.semantic_tokens + 3
 
   vim.api.nvim_buf_set_extmark(bufnr, state.namespace, token.line, token.start_col, {
     hl_group = hl_group,

runtime/lua/vim/lsp/util.lua

@@ -2,7 +2,6 @@ local protocol = require('vim.lsp.protocol')
 local validate = vim.validate
 local api = vim.api
 local list_extend = vim.list_extend
-local highlight = vim.highlight
 local uv = vim.uv
 
 local M = {}
@@ -1716,13 +1715,13 @@ do --[[ References ]]
         [protocol.DocumentHighlightKind.Write] = 'LspReferenceWrite',
       }
       local kind = reference['kind'] or protocol.DocumentHighlightKind.Text
-      highlight.range(
+      vim.hl.range(
         bufnr,
         reference_ns,
         document_highlight_kind[kind],
         { start_line, start_idx },
         { end_line, end_idx },
-        { priority = vim.highlight.priorities.user }
+        { priority = vim.hl.priorities.user }
       )
     end
   end