[flex] Plumb two bools via the FlexItem struct.

Previously we'd recalculate IsUsedFlexBasisDefinite many times when
we can just compute it once, and pass it around via the FlexItem
structs.

This patch introduces two fields:
  is_used_flex_basis_indefinite
  is_initial_block_size_indefinite

To do this. After this patch there is only one callsite to both:
  IsUsedFlexBasisDefinite
  AspectRatioProvidesMainSize

The final methods which are using the bad "Unresolvable" functions.

There should be no behaviour change.

Bug: 328572265
Change-Id: I57561172e7af55253904719a7f5f6a3cde8db42b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5385672


Reviewed-by: David Baron <dbaron@chromium.org>
Commit-Queue: Ian Kilpatrick <ikilpatrick@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1276873}