[Impeller] Implement TextDecoration (i.e. dashed lines)

[matanlurey]

Closes flutter/flutter#126673.

Ideally, this would be an #ifdef, but currently Impeller is a runtime flag, for reasons (CI capacity?)

To be able to write tests, I'd need flutter/flutter#133264 completed. Edit:

Before

After

[flutter-dashboard]

It looks like this pull request may not have tests. Please make sure to add tests before merging. If you need an exemption to this rule, contact Hixie on the #hackers channel in Chat (don't just cc him here, he won't see it! He's on Discord!).

If you are not sure if you need tests, consider this rule of thumb: the purpose of a test is to make sure someone doesn't accidentally revert the fix. Ask yourself, is there anything in your PR that you feel it is important we not accidentally revert back to how it was before your fix?

Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing.

[jonahwilliams]

LGTM with nits, and caveat that this isn't a naive implementation its just... the only reasonable way to draw a dashed line with the impeller backend.

[chinmaygarde]

@jonahwilliams Looks good for another review.

[jonahwilliams]

We're working on finding a way to test this on CI.

[matanlurey]

Ready again for review, thanks @jonahwilliams and @jason-simmons!

[matanlurey]

It looks like I'm using a library (dl_op_spy.h) that I shouldn't be using in this test (or it should be moved into its own source set), which in turn is causing various failures:

ld64.lld: error: undefined symbol: Dart_TimelineGetMicros
>>> referenced by animator.cc:126 (../../flutter/shell/common/animator.cc:126)
>>>               obj/flutter/shell/common/common.animator.o:(symbol flutter::Animator::BeginFrame(std::_LIBCPP_ABI_NAMESPACE::unique_ptr<flutter::FrameTimingsRecorder, std::_LIBCPP_ABI_NAMESPACE::default_delete<flutter::FrameTimingsRecorder>>)::$_0::operator()() const+0x38)
>>> referenced by dart_vm.cc:474 (../../flutter/runtime/dart_vm.cc:474)
>>>               obj/flutter/runtime/runtime.dart_vm.o:(symbol flutter::DartVM::DartVM(std::_LIBCPP_ABI_NAMESPACE::shared_ptr<flutter::DartVMData const> const&, std::_LIBCPP_ABI_NAMESPACE::shared_ptr<flutter::IsolateNameServer>)+0x9f8)
>>> referenced by dart_vm_initializer.cc:101 (../../flutter/runtime/dart_vm_initializer.cc:101)
>>>               obj/flutter/runtime/runtime.dart_vm_initializer.o:(symbol DartVMInitializer::Initialize(Dart_InitializeParams*, bool, bool)+0x1bc)
>>> referenced 2 more times

[jonahwilliams]

LGTM