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

@@ -23,7 +23,7 @@ function! ale#cursor#TruncatedEcho(original_message) abort
     " Change tabs to spaces.
     let l:message = substitute(l:message, "\t", ' ', 'g')
     " Remove any newlines in the message.
-    let l:message = substitute(l:message, "\n", '', 'g')
+    let l:message = substitute(l:message, "\n", ' ', 'g')
     " Convert indentation groups into single spaces for better legibility when
     " put on a single line
     let l:message = substitute(l:message, ' \+', ' ', 'g')
@@ -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,