Rename BOUNDS_CHECKED pragma to CHECKED_SCOPE.

[dtarditi]

• Rename pragma and associated methods within the compiler.
• Update tests
• There are corresponding PRs for Checked C and the Checked C LNT repos: Rename BOUNDS_CHECKED pragma to CHECKED_SCOPE. checkedc#282 and Replace BOUNDS_CHECKED pragma with CHECKED_SCOPE. microsoft/checkedc-llvm-test-suite#86.

Testing:

• Passed local testing on Windows and automated testing on Linux.

[dtarditi]

@nmeum, flagging that this compiler change will require changes in your code base.