[FR] Add symbol search support to files without a extension

[brendan-kellam]

In SB, files without a extension can be mapped to a linguist language by using the linguist-language override in a .gitattributes file (docs). This enables features like syntax highlighting to work.

However, this does not work for symbol search. At index time, universal ctags is not reading from .gitattributes and therefore does not resolve symbols for the file as it does not know the language.