Add option to customize length of symbols for make_entry.gen_from_treesitter

[mjendruk]

Description

This adds the same options which already exist for gen_from_lsp_symbols to control the allocated space for symbols in make_entry.gen_from_treesitter.

Added options:

• symbol_width: controls the space for the symbol (defaults to 25)

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

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

• Simply provide symbol_width as an option and observe how the space for the symbol in the treesitter picker grows and shrinks.

Configuration:

• Neovim version (nvim --version): 0.9.5
• Operating system and version: Linux

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]

closes #3041

thanks!