Add '.' in GPR language server's triggerCharacters

And adapt the tests accordingly, formatting them too.

For eng/ide/ada_language_server#1398

Author: AnthonyLeonardoGracio

source/gpr/lsp-gpr_handlers.adb

@@ -381,7 +381,7 @@ package body LSP.GPR_Handlers is
       Capabilities.declarationProvider := LSP.Constants.True;
       Capabilities.completionProvider :=
         (Is_Set => True,
-         Value  => (triggerCharacters => [" "],
+         Value  => (triggerCharacters => [" ", "."],
                     resolveProvider   => LSP.Constants.True,
                     others            => <>));