fix(help_tags): show help tags on windows (#3126)

[xudyang1]

On Windows, builtin.help_tags picker does not show any help tags.

To fix this, the following changes are needed:

1. util.path_tail checks unix separator / on Windows and leave the original implementation intact on unix systems.

2. Line endings should be taken carefully on Windows. vim.split with only newline \n character as separator may result in unexpected crash when parsing large files. When splits on lines are needed, call it with \r?\n, or even set up a wrapper function in utils is more prefered.

Fixes #3126

Description

Please include a summary of the change and which issue is fixed. Please also
include relevant motivation and context

Fixes #3126 (issue)

Type of change

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• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list relevant details about your configuration

• util.path_tail on Windows, Linux, and MacOS
• util.split_lines on Windows, Linux and MacOS

Configuration:

• Neovim version (nvim --version): 0.10.0
• Operating system and version: Windows 10 22H2

Checklist:

• My code follows the style guidelines of this project (stylua)
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (lua annotations)

[jamestrew]

Thanks, I'll try to take a closer look in the coming days.

[jamestrew]

Couple of minor things but otherwise looks good to me. Gave all the touched pickers/previewers a try and they work for me (at least on linux).

[jamestrew]

Thanks a lot!