[lldb/formatter] Add Swift.UnsafeBufferPointer data formatter

[medismailben]

This patch adds support for Swift's UnsafeBufferPointer and
UnsafeMutableBufferPointer data formatting.

It introduces a summary provider and a synthetic frontend creator for
these types.

Signed-off-by: Med Ismail Bennani [email protected]

[medismailben]

@swift-ci test

[dcci]

Thanks for taking care of this. While I think the logic is mostly correct, this opens the opportunity to do some things better. I outlined some of my concerns inline.

[medismailben]

I updated the patch to address @dcci and @fredriss comments:

• I reimplemented the logic to read the entire contiguous buffer once (instead of doing a read per entry). I also added support for complex generic types like struct and enum and added comments and documentation to explain the 'value-providing synthetic children' workaround and clarify the UnsafeBufferPointer structure layout.
• As suggested, I unified the mutable and immutable data-formatter registration.
• Finally, I rewrote the test to prevent the UB, did some cleanup and added more test cases.

[medismailben]

@swift-ci test

[medismailben]

@swift-ci test

[medismailben]

@swift-ci test

[medismailben]

Added more tests (value associated enums, generic class, existential type (archetypes) ...)
Addressed recent feedbacks.
Removed copyright header in tests.

[medismailben]

The macOS failure happened on a Swift test. Given that I only touched to LLDB, I assume this is a flaky test.

[medismailben]

@swift-ci test macOS Platform

[medismailben]

swiftlang/swift#32152 Should fix the test failure. Let's try re-running the macOS CI again!

[medismailben]

@swift-ci test macOS Platform

[fredriss]

After you address this last round of comments, this LGTM

[medismailben]

@swift-ci test

[medismailben]

@swift-ci test macOS Platform