runtime(javascript): Add "using" keyword to JavaScript syntax highlighting

runtime(javascript): Add "using" keyword to JavaScript syntax highlighting

Prior to this change, const and let were keywords for variable
declarations.

This change adds `using` as another keyword for variable declaration.

This JavaScript feature was recently introduced.

Docs:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/using

closes: #18381

Signed-off-by: Devin Weaver <suki@tritarget.org>
Signed-off-by: Christian Brabandt <cb@256bit.org>