add lsp format operator mapping (#546)

* add lsp format operator mapping

* document normal mode lspformat mapping

* convert legacy to vim9 script

doc/lsp.txt

@@ -815,7 +815,8 @@ can map these commands to keys and make it easier to invoke them.
 			current buffer are used when format is applied.
 
 :{range}LspFormat	Format the specified range of lines in the current
-			file using the language server.
+			file using the language server. Map <plug>(LspFormat)
+			in normal mode to operate on text objects.
 
 						*:LspGotoDeclaration*
 :[count]LspGotoDeclaration

plugin/lsp.vim

@@ -74,7 +74,19 @@ command! -nargs=0 -bar LspDiagShow lsp.ShowDiagnostics()
 command! -nargs=0 -bar LspDiagHere lsp.JumpToDiag('here')
 command! -nargs=0 -bar LspDocumentSymbol lsp.ShowDocSymbols()
 command! -nargs=0 -bar LspFold lsp.FoldDocument()
+
 command! -nargs=0 -bar -range=% LspFormat lsp.TextDocFormat(<range>, <line1>, <line2>)
+def LspFormatFunc(type: string, visual_mode = v:false)
+  if visual_mode
+    exe "normal! gv:LspFormat\<cr>"
+  elseif type ==# 'line'
+    exe "normal! '[V']:LspFormat\<cr>"
+  elseif type ==# 'char'
+    exe "normal! `[v`]:LspFormat\<cr>"
+  endif
+enddef
+nnoremap <silent> <plug>(LspFormat)  <Cmd>set operatorfunc=LspFormatFunc<cr>g@
+
 command! -nargs=0 -bar -count LspGotoDeclaration lsp.GotoDeclaration(v:false, <q-mods>, <count>)
 command! -nargs=0 -bar -count LspGotoDefinition lsp.GotoDefinition(v:false, <q-mods>, <count>)
 command! -nargs=0 -bar -count LspGotoImpl lsp.GotoImplementation(v:false, <q-mods>, <count>)