Implement LSP symbol search

test/lsp/test_lsp_client_messages.vader

@@ -161,6 +161,17 @@ Execute(ale#lsp#message#References() should return correct messages):
   \ ],
   \ ale#lsp#message#References(bufnr(''), 12, 34)
 
+Execute(ale#lsp#message#Symbol() should return correct messages):
+  AssertEqual
+  \ [
+  \   0,
+  \   'workspace/symbol',
+  \   {
+  \     'query': 'foobar',
+  \   }
+  \ ],
+  \ ale#lsp#message#Symbol('foobar')
+
 Execute(ale#lsp#message#Hover() should return correct messages):
   AssertEqual
   \ [

test/lsp/test_other_initialize_message_handling.vader

@@ -16,6 +16,7 @@ Before:
   \   'completion': 0,
   \   'completion_trigger_characters': [],
   \   'definition': 0,
+  \   'symbol_search': 0,
   \ },
   \}
 
@@ -67,7 +68,8 @@ Execute(Capabilities should bet set up correctly):
   \     },
   \     'definitionProvider': v:true,
   \     'experimental': {},
-  \     'documentHighlightProvider': v:true
+  \     'documentHighlightProvider': v:true,
+  \     'workspaceSymbolProvider': v:true
   \   },
   \ },
   \})
@@ -80,6 +82,7 @@ Execute(Capabilities should bet set up correctly):
   \   'references': 1,
   \   'hover': 1,
   \   'definition': 1,
+  \   'symbol_search': 1,
   \ },
   \ b:conn.capabilities
 
@@ -121,6 +124,7 @@ Execute(Disabled capabilities should be recognised correctly):
   \   'references': 0,
   \   'hover': 0,
   \   'definition': 0,
+  \   'symbol_search': 0,
   \ },
   \ b:conn.capabilities