test: add missing context tests for existing queries

[PeterCardenas]

With #567, it is revealed that many queries are missing their respective context test files. With this, I wanted to go through the clean up of adding a context test for each existing query (with the exception of php_only and ocaml_interface). I also moved what seems to me are snapshot tests into their own directory to remove confusion between the purposes of the files and snapshot test failures. Through this exercise, I found that the tests are lacking in a couple of areas that I'll clean up in future PRs:

• injected languages are not currently tested with this method. what i imagine i'll do here is check the parser tree and get the children languages to index the test files by relevant injected languages.
• when no treesitter parsers are installed, many context tests are skipped the first time the suite is run. i'll see what i can do with the treesitter api here.
• multiline contexts sometimes require only one line to be marked with {{CONTEXT}}. it would make much more sense for me to mark all of the relevant lines. it would also be more immediately apparent for the person introducing the query if the multiline query is accepting too much (which is currently the problem with some languages)