Language server doesn't work on newly created non-.ino files

[per1234]

Describe the bug

When a tab is created for a .cpp, .c, or .h file, no language server capabilities work in it. It only starts working after closing and reopening the sketch or changing the board selection.

To Reproduce

1. Open a sketch in the Arduino IDE.
2. Click the downward pointing triangle button on the right side of the tab bar.
3. Select "New Tab" from the menu.
4. In the "Name for new file" field, type foo.cpp.
5. Click the OK button.
6. Add some code to the foo.cpp tab that should produce some reaction from the language server. For example, this code:

   asdf

   should produce a red squiggly underline.
   Note that there is no language server capabilities in the file.
7. Close the sketch.
8. Open the sketch again.
   Note that the language server capabilities are now working as expected in foo.cpp.

Expected behavior

Language Server capabilities work in all types of sketch code files from creation on.

Desktop

• OS: Windows 10
• Arduino IDE Version: 2.0.0-rc2
  Date: 2021-12-13T10:09:39.122Z
  CLI Version: 0.20.2 [13783819]

Additional context

The issue does not occur when using Arduino Language Server version 0.5.0-rc2

Logs:
LSnew.zip