Only strip newlines for echo, otherwise full messages (#4964)

* Updates `ale#lsp#response#ReadDiagnostics` to always store the full, unaltered diagnostic message from the LSP in question. The current process is to replace all newline characters with whitespace (' '), which then leads to broken formatting when viewing complex output from an LSP with `:ALEDetail` and other commands.
* Updates `ale#cursor#TruncatedEcho` to replace newline characters with a space ' ' instead of an empty string '' to retain the previous style of formatting for echoed messages.

Fixes: #2356
Fixes: #3068
Fixes: #2301

autoload/ale/cursor.vim

@@ -93,6 +93,7 @@ function! ale#cursor#EchoCursorWarning(...) abort
         if !empty(l:loc)
             let l:format = ale#Var(l:buffer, 'echo_msg_format')
             let l:msg = ale#GetLocItemMessage(l:loc, l:format)
+
             call ale#cursor#TruncatedEcho(l:msg)
             let l:info.echoed = 1
         elseif get(l:info, 'echoed')

autoload/ale/lsp/response.vim

@@ -28,7 +28,7 @@ function! ale#lsp#response#ReadDiagnostics(diagnostics) abort
     for l:diagnostic in a:diagnostics
         let l:severity = get(l:diagnostic, 'severity', 0)
         let l:loclist_item = {
-        \   'text': substitute(l:diagnostic.message, '\(\r\n\|\n\|\r\)', ' ', 'g'),
+        \   'text': l:diagnostic.message,
         \   'type': 'E',
         \   'lnum': l:diagnostic.range.start.line + 1,
         \   'col': l:diagnostic.range.start.character + 1,

test/lsp/test_read_lsp_diagnostics.vader

@@ -109,11 +109,11 @@ Execute(ale#lsp#response#ReadDiagnostics() should include sources in detail):
   \   }
   \ ])
 
-Execute(ale#lsp#response#ReadDiagnostics() should keep detail with line breaks but replace with spaces in text):
+Execute(ale#lsp#response#ReadDiagnostics() should keep line breaks in text):
   AssertEqual [
   \   {
   \     'type': 'E',
-  \     'text': 'cannot borrow `cap` as mutable more than once at a time  mutable borrow starts here in previous iteration of loop',
+  \     'text': "cannot borrow `cap` as mutable\r\nmore than once at a time\n\nmutable borrow starts here\rin previous iteration of loop",
   \     'detail': "[rustc] cannot borrow `cap` as mutable\r\nmore than once at a time\n\nmutable borrow starts here\rin previous iteration of loop",
   \     'lnum': 10,
   \     'col': 15,

test/test_cursor_warnings.vader

@@ -30,7 +30,7 @@ Before:
   \       'nr': -1,
   \       'type': 'E',
   \       'code': 'semi',
-  \       'text': "Missing semicolon.\r",
+  \       'text': "Missing\nsemicolon.\r",
   \       'detail': "Every statement should end with a semicolon\nsecond line",
   \     },
   \     {