[Feature Request] Add custom file extension / language associations for Syntax Highlighting

[evilbaschdi]

Problem

Many tools use custom file extensions for standard file formats (e.g., .xrm or .vsconfig for JSON, .axaml or .slnx for XML).

Currently, SourceGit doesn't recognize these custom extensions as standard JSON/XML - or most of them, which affects syntax highlighting in the diff/file viewer. Hardcoding these extensions directly into SourceGit wouldn't be maintainable long-term.

Proposed Solution

Implement a customizable file association mapping similar to VS Code's files.associations setting.

VS Code handles this cleanly through files.associations, allowing users to seamlessly map glob patterns or custom extensions to built-in language parsers.

"files.associations": {
        "*.axaml": "xml",
        "*.DotSettings": "xml",
        "*.fakes": "xml",
        "*.lutconfig": "xml",
        "*.ncrunchproject": "xml",
        "*.ncrunchsolution": "xml",
        "*.osts": "ts",
        "*.pssproj": "xml",
        "*.slnx": "xml",
        "*.user": "xml",
        "*.vbm": "xml",
        "*.vsconfig": "json",
        "*.vsext": "json",
        "*.vsixmanifest": "xml",
        "*.xrm": "json",
        "*.xrm2": "json",
        "*.xrmconfig": "json",
        "*.xrmsuo": "json",
        "Bookmarks*": "json"
    }

This could be configured via preference.json (or exposed in the Preference window).

[evilbaschdi]

Maybe something like develop...evilbaschdi:sourcegit:develop

...while custom_fileassociations.json looks like

{
    "associations": {
        ".DotSettings": ".xml",
        ".fakes": ".xml",
        ".lutconfig": ".xml",
        ".ncrunchproject": ".xml",
        ".ncrunchsolution": ".xml",
        ".osts": ".ts",
        ".pssproj": ".xml",
        ".slnx": ".xml",
        ".user": ".xml",
        ".vbm": ".xml",
        ".vsconfig": ".json",
        ".vsext": ".json",
        ".vsixmanifest": ".xml",
        ".xrm": ".json",
        ".xrm2": ".json",
        ".xrmconfig": ".json",
        ".xrmsuo": ".json",
        ".runsettings": ".xml",
        "Bookmarks*": ".json"
    }
}

[evilbaschdi]

#2728