Fix end position of diagnostic for LSP

Follow up rubocop/rubocop#12932.

This is a porting because it can be said that even Standard.rb, which serves as the base for RuboCop's built-in LSP,
does the same thing.

---

This is a quote from rubocop/rubocop#12932.

`character` of `Position` is zero-based
https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#position
> Character offset on a line in a document (zero-based).

And, `Parser::Source::Range` is also zero-based
https://github.com/whitequark/parser/blob/3e260d2e37bcb3de8705489d1c2799c26c7a2215/lib/parser/source/range.rb#L104
> zero-based column number of the end of this range.

Therefore, `-1` is not necessary.

lib/standard/lsp/routes.rb

@@ -181,7 +181,7 @@ def diagnostic(file_uri, text)
             message: msg,
             range: {
               start: {character: loc[:start_column] - 1, line: loc[:start_line] - 1},
-              end: {character: loc[:last_column] - 1, line: loc[:last_line] - 1}
+              end: {character: loc[:last_column], line: loc[:last_line] - 1}
             },
             severity: severity,
             source: "standard"

test/standard/runners/lsp_test.rb

@@ -45,17 +45,17 @@ def test_did_open
         diagnostics: [
           {code: "Layout/ArrayAlignment",
            message: "Use one level of indentation for elements following the first line of a multi-line array.",
-           range: {start: {character: 3, line: 2}, end: {character: 3, line: 2}},
+           range: {start: {character: 3, line: 2}, end: {character: 4, line: 2}},
            severity: 3,
            source: "standard"},
           {code: "Layout/ExtraSpacing",
            message: "Unnecessary spacing detected.",
-           range: {start: {character: 4, line: 2}, end: {character: 4, line: 2}},
+           range: {start: {character: 4, line: 2}, end: {character: 5, line: 2}},
            severity: 3,
            source: "standard"},
           {code: "Layout/SpaceInsideArrayLiteralBrackets",
            message: "Do not use space inside array brackets.",
-           range: {start: {character: 4, line: 2}, end: {character: 5, line: 2}},
+           range: {start: {character: 4, line: 2}, end: {character: 6, line: 2}},
            severity: 3,
            source: "standard"}
         ],