Fix many typos

[Sajjon]

Description

I opened a PR with typo fixes in 500+ files. We have agreed it was too big a PR so we decided to split it up. This issue supersedes the original PR and can be used to track the same set of changes but now across multiple PRs:

The set of changes have been split into these PRs, split by folders in the Swift compiler project:

• PR for changes to lib and include (lib and include part of the same PR, as suggested by @compnerd here)
• ✅ PR for changes to Benchmark folder
• ✅ PR for changes to docs
• ✅ PR for changes to stdlib
• ✅ PR for changes to SwiftCompilerSources
• PRs for changes to test
  • ✅ test/IDE
  • ✅ test/SourceKit
  • ✅ test/SILOptimizer
  • ✅ test/SILGen
  • ✅ test/IRGen
  • ✅ test/Concurrency
  • ✅ test/interop
  • test/* (misc)
• ✅ All the rest / misc