Pretty-print lets with surrounding braces

[RyanGlScott]

The pretty-printer for letseq and letrec was not adding braces around the variables being bound, resulting in malformed pretty-printed output such as letseq hw = "Hello, World!";; .... After adding braces, this now becomes letseq { hw = "Hello, World!"; };, which is valid Bluespec code. Fixes #529.

In order to add a test case for this fix, I needed to add some machinery to the test suite to run bsv2bsc, which exercises the relevant code paths. Along the way, I fixed a bug in the bsc2bsv machinery (on which the bsv2bsc machinery is based), so this PR also fixes #531.

[RyanGlScott]

As discussed in #529 (comment), a more direct way to test these changes is to use bsc's -dparsed=<filename> approach, which makes use of bsc's prettyprinter without needing to use the internal bsv2bsc tool. I'll mark this PR as a draft until I get that set up.

I'll plan to revert the changes in this PR involving bsv2bsc. That being said, this PR also contains a fix for #531, which is useful independent of this PR. I've opened #533 (a separate PR) for that.

[RyanGlScott]

I've pushed a new version that uses the -dparsed=<filename> option to test the fix.

[quark17]

Merged! Thanks!

FYI, I made two changes before merging: I changed the file name to be descriptive of the feature that it's testing (the fact that it's related to a GitHub issue is conveyed in a comment in the .exp file), and I changed the module name. The latter change is not so important, but figured I'd tweak it to follow the convention used in most of the newer test files (that the module name should be predictable from the file name).