Feat: Support localleader (#3382)

[dheerusri324]

What this PR does / why we need it:
This PR adds support for the <localleader> keymap, acting analogously to the existing <leader> configuration.

In Vim, <localleader> provides a prefix key for buffer-local or filetype-local mappings (often , or \), separate from the global <leader>. Users often rely heavily on these mappings in their existing .vimrc configurations, and previously, they could not easily port those configurations into VSCodeVim without manual translations.

This PR implements <localleader> across the entire codebase to mirror the precise functionality of <leader>, including:

• Exposing the vim.localleader extension setting (\ by default, same as Vim).
• Resolving <localleader> securely through key normalization (Notation.NormalizeKey) and execution action loops (CompareKeypressSequence).
• Integrating with the .vimrc Vimscript parser so <localleader> is fully supported in user map configurations.
• Accurately processing <localleader> replacement during UI rendering (showcmd status).
• Enabling TextMate syntax highlighting for <LocalLeader> within .vim files.

Which issue(s) this PR fixes

fixes #3382

Special notes for reviewer:

• All changes strictly adhere to the pre-existing <leader> implementation structure. NormalizeKey and printableKey have updated signatures to accept an optional third argument for localLeaderKey.
• Inside recordedState.ts getters, localleader display replacements explicitly run before leader replacements conditionally to prevent collision clobbering when both variables default to the identical \ key sequence.
• Tested the integration locally in both normal user configuration bounds and custom remapping contexts to verify functionality.