Add grammar tests for handling + + and - - operations

[xpyctumo]

Issue

Closes #1267

Checklist

• I have updated CHANGELOG.md
• I have run all the tests locally and no test failure was reported
• I have run the linter, formatter and spellchecker
• I did not do unrelated and/or undiscussed refactorings

[xpyctumo]

<unknown>:2:28: Expected not "-"

    Line 2, col 28:
      1 | contract Foo {
    > 2 |     a: Int as coins = 123 - -456;
                                     ^
      3 |     b: Int as coins = 123 + -456;

      18 |         // eslint-disable-next-line @typescript-eslint/no-explicit-any
      19 |         const message = `Expected ${(matchResult as any).getExpectedText()}\n`;
    > 20 |         throw new TactCompilationError(display.at(source, message), source);
         |               ^
      21 |     },
      22 | });

The old parser will return this error.
Is it possible for us to somehow separate the new/old parser and tests now?

[xpyctumo]

Is it possible for us to somehow separate the new/old parser and tests now?

Tests moved to src/grammar/next/test directory. They will only run using the new parser