refactor: invert some conditionals for better readability

[agilgur5]

Summary

Small refactor to invert some conditionals/if statements for better readability

• handful of refactors I'm making as I'm now very familiar with the codebase to make it easier to work with and more approachable to new contributors as well

Details

• a few if (cond) { big block } return could be inverted to if (!cond) return then the block un-indented instead

  • generally speaking, this makes it a lot more readable (less indentation, etc) and follows the existing code style in much of the codebase, where it's a few quick one-line ifs and then just the rest of the code

• shorten the resolvedFileName conditional by using optional chaining

  • prefer the simpler x?.y over the older x && x.y syntax

• add a resolved variable for less repetition of the whole statement

• add a comment to the pathNormalize line about why it's used in that one place and link to the longer description in the PR as well

• shorten comment about useTsconfigDeclarationDir so it doesn't take up so much space or look so important as a result

  • it's easier to read this way and I made the explanation less verbose and quicker to read too
  • already have comments and lines in the codebase longer than 80 chars, so that's not a guideline that's followed anywhere else

• remove the else there and just add an early return instead, similar to the inverted conditionals above

  • similarly makes it less unindented, more readable etc

Review Notes

• This is unfortunately going to merge conflict with fix: don't attempt to change declarationMap sources when no output #334 as one of the conditionals is changed there as well, so I'll need to rebase this once that's fixed

• Ignoring whitespace changes makes this PR easier to read

[agilgur5]

I was looking through some old tabs and saw that CodeClimate actually defines a term for this kind of complexity. "Cognitive Complexity" includes complexity due to nesting.

Great to have a term for what I was describing moving forward!