NVDA 2026.2 readiness: support custom speech dictionary definitions in the add-on template and scons tools

[josephsl]

Hi,

This issue stems from nvaccess/nvda#17468:

NVDA 2026.2 allows add-ons to include custom speech dictionaries. This allows add-ons to include custom pronunciations, useful if an add-on improves support for apps with custom abbreviations and symbols that require custom speech dictionary rules/replacements. Therefore, I would like to propose adding custom speech dictoinaries definitions support to add-on template, specifically definition and generation of speech ictionaries manifest key via scons tools.

Thakns.