Add syntax highlighting for dispose blocks and fix test assertions

[Copilot]

The initial implementation for dispose block syntax highlighting failed CI due to misaligned token assertions in the test suite and an outdated compiled JSON grammar file.

Changes

• Keyword support: Added dispose to the named block control keyword regex in PowerShellSyntax.tmLanguage, properly integrating it alongside the newly added clean block.
• Test assertion alignment: Corrected the syntax in spec/testfiles/syntax_test_Function.ps1 by adding a space before the brace (Dispose {). This ensures the atom-grammar-test column pointers correctly align with the parsed token boundaries.
• Grammar compilation: Regenerated the powershell.tmLanguage.json file so the tests run against the updated regex patterns.

Example

function Get-Foo {
    [CmdletBinding()]
    param()

    begin { }
    process { }
    end { }
    clean { }
    dispose { } # Now correctly highlighted as keyword.control.powershell
}