Fix URI parsing/formatting

[jakebailey]

Fixes #932

These tests are from vscode-uri.

I suspect this isn't perfect, but I think this is sufficient as a stop-gap to fix the major problems without porting vscode-uri itself.

[Copilot]

Pull Request Overview

This PR fixes URI parsing/formatting issues, addressing major problems without fully porting vscode-uri.

• Renames the volume character detection function from isVolumeCharacter to IsVolumeCharacter for export.
• Adds helper functions (fixWindowsURIPath, splitVolumePath) to support Windows URI path parsing.
• Updates URI conversion functions and introduces comprehensive test coverage in converters_test.go.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
internal/tspath/path.go	Renamed helper function for volume detection and updated call-sites accordingly.
internal/ls/converters_test.go	Added tests for DocumentURIToFileName and FileNameToDocumentURI covering various cases.
internal/ls/converters.go	Revised URI conversion logic with Windows path handling and enhanced escaping.