Fix some lints

[etiennebacher]

Hello, I'm building a new package to find and automatically fix lints in R code: flint.

I'm using real-life, large packages to check its performance and rlang is one of them. Since I already test on this, there's no additional cost for me in proposing those changes.

FYI, those changes were generated with flint::fix_package() (with a few corner cases removed by hand because I need to address them in flint).

There are many changes but most of them are trivial:

• replace any(is.na()) by anyNA()
• add a leading 0 to decimal (e.g .1 -> 0.1)
• use expect_named(), expect_null(), and friends in tests
  etc.

flint is quite new and linter rules are necessarily a bit opinionated, so some of those changes might not be to your taste, but I'd be happy to have some feedback on this.