Lower confidence for short patterns (D3 and NV3D patterns) (#1854)

* Low confidence for 2-character environment variables

These can be automatically generated by the Google Closure Compiler
(which will, if configured, replace global variables with auto-generated
ones such as aa, ab, ac et cetera.) Hence, they are a less reliable
indication that a library which would also set said variable is present.

* Low confidence for D3 and NV3D env patterns

These variables can be automatically generated by the Google Closure Compiler (which will, if configured, replace global variables with auto-generated ones such as aa, ab, ac et cetera.) Hence, they are a less reliable indication that a library which would also set said variable is present.