mergetools: vscode: new tool

VSCode has supported three-way merges since 2022, see
<microsoft/vscode#5770 (comment)>.

Although the program binary is located at /usr/bin/code, name the
mergetool "vscode" because the word "code" is too generic and would lead
to confusion. The name "vscode" also matches Git's existing
contrib/vscode directory.

On Windows, VSCode adds the directory that contains code.cmd to %PATH%,
so there is no need to invoke mergetool_find_win32_cmd to search for the
program.

Signed-off-by: Alex Henrie <alexhenrie24@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

mergetools/vscode

@@ -0,0 +1,19 @@
+diff_cmd () {
+	"$merge_tool_path" --wait --diff "$LOCAL" "$REMOTE"
+}
+
+diff_cmd_help () {
+	echo "Use Visual Studio Code (requires a graphical session)"
+}
+
+merge_cmd () {
+	"$merge_tool_path" --wait --merge "$REMOTE" "$LOCAL" "$BASE" "$MERGED"
+}
+
+merge_cmd_help () {
+	echo "Use Visual Studio Code (requires a graphical session)"
+}
+
+translate_merge_tool_path () {
+	echo code
+}