Based on the work by Enrique Moreno Tent on Github.

Features

• Some additional keywords like FLUIDTEMPLATE.
• Added the ability to comment and uncomment via Sublime Text functionality (menu and keyboard).
• Highlighting for TypoScript conditions
• Highlighting for deprecated keywords (TYPO3 7.x)

Supported files

The package will apply the syntax automatically to files to *.ts, *.ts2, *.t3, *.t3c, *.t3s files.

By installing the ApplySyntax package some of TYPO3s *.txt files are covered as well:

• ext_conf_template.txt
• ext_typoscript_constants.txt
• ext_typoscript_setup.txt
• constants.txt (*)
• setup.txt (*)

*) As long as their paths contain the strings fileadmin, typo3 or TypoScript.

The ApplySyntax configuration actually looks like this:

{
    "syntaxes": [
        {
            "syntax": "TypoScript/TypoScript",
            "rules": [
                {"file_path": ".*(\\\\|/)ext_conf_template\\.txt$"},
                {"file_path": ".*(\\\\|/)ext_typoscript_(setup|constants)\\.txt$"},
                {"file_name": ".*(\\\\|/)(fileadmin|typo3|TypoScript).*(\\\\|/)(setup|constants)\\.txt$"},
                {"file_path": ".*(\\\\|/)Configuration(\\\\|/)TypoScript(\\\\|/).*\\.txt$"}
            ]
        }
    ]
}

To apply TypoScript syntax highlighting to other files you could easily enhance the above syntax detection rules. Have a look into the ApplySyntax manual

Thanks to Philipp Kitzberger and Mathias Brodala for the hint.