Use the is_absolute_containing_block method everywhere

[mrobinson]

This is a better approach than relying on
contains_positioned_fragments, because in the future other properties
will create absolute containing blocks.

---

• ./mach build -d does not report any errors
• ./mach test-tidy does not report any errors
• These changes fix #__ (github issue number if applicable).

• There are tests for these changes OR
• These changes do not require tests because they do not change behavior.

---

This change is 

[highfive]

Heads up! This PR modifies the following files:

• @emilio: components/layout/block.rs, components/layout/construct.rs, components/layout/inline.rs, components/layout/flow.rs

[highfive]

Warning

• These commits modify layout code, but no tests are modified. Please consider adding a test!

[jdm]

r? @mbrubeck

[mbrubeck]

@bors-servo r+

[bors-servo]

📌 Commit 0a24c2f has been approved by mbrubeck

[bors-servo]

⌛ Testing commit 0a24c2f with merge 91f9a0c...

[bors-servo]

💔 Test failed - android

[mrobinson]

Hrm. This build failure doesn't look like it is related to this PR:

thread '<unnamed>' panicked at 'called `Option::unwrap()` on a `None` value', /checkout/src/libcore/option.rs:335:20
stack backtrace:
   0: std::sys::imp::backtrace::tracing::imp::unwind_backtrace
             at /checkout/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::_print
             at /checkout/src/libstd/sys_common/backtrace.rs:71
   2: std::panicking::default_hook::{{closure}}
             at /checkout/src/libstd/sys_common/backtrace.rs:60
             at /checkout/src/libstd/panicking.rs:380
   3: std::panicking::default_hook
             at /checkout/src/libstd/panicking.rs:396
   4: std::panicking::rust_panic_with_hook
             at /checkout/src/libstd/panicking.rs:610
   5: std::panicking::begin_panic
             at /checkout/src/libstd/panicking.rs:571
   6: std::panicking::begin_panic_fmt
             at /checkout/src/libstd/panicking.rs:521
   7: rust_begin_unwind
             at /checkout/src/libstd/panicking.rs:497
   8: core::panicking::panic_fmt
             at /checkout/src/libcore/panicking.rs:71
   9: core::panicking::panic
             at /checkout/src/libcore/panicking.rs:51
  10: __rust_maybe_catch_panic
             at /checkout/src/libcore/macros.rs:32
             at /checkout/src/libpanic_unwind/gcc.rs:101
             at /checkout/src/libpanic_unwind/lib.rs:101
  11: <F as alloc::boxed::FnBox<A>>::call_box
  12: std::sys::imp::thread::Thread::new::thread_start
             at /checkout/src/liballoc/boxed.rs:692
             at /checkout/src/libstd/sys_common/thread.rs:21
             at /checkout/src/libstd/sys/unix/thread.rs:84
  13: start_thread
  14: clone
fatal runtime error: failed to initiate panic, error 5
error: Could not compile `script`.

[jdm]

@bors-servo: retry

• #18116

[bors-servo]

⌛ Testing commit 0a24c2f with merge 7806784...

[bors-servo]

☀️ Test successful - android, arm32, arm64, linux-dev, linux-rel-css, linux-rel-wpt, mac-dev-unit, mac-rel-css1, mac-rel-css2, mac-rel-wpt1, mac-rel-wpt2, mac-rel-wpt3, mac-rel-wpt4, windows-msvc-dev
Approved by: mbrubeck
Pushing 7806784 to master...