[MemoryCache] Introduce intelligent, value-based cache pruning

This CL introduces a more sophisticated, value-based pruning strategy
for the in-memory resource cache, gated by the
kMemoryCacheIntelligentPruning feature flag.

The existing strong reference cache uses a simple LRU (Least Recently
Used) eviction strategy. This can lead to suboptimal outcomes where a
large, critical resource (e.g., a core stylesheet) might be evicted to
make room for less important, more recently accessed resources.

This new strategy calculates a "value" for each resource to make more
intelligent eviction decisions. The value is a weighted score based on
three factors:
- Resource Type: Critical resources like CSS and fonts are given a higher intrinsic priority.
- Usage Frequency: The MemoryCacheHitCount is now tracked and used, scaled logarithmically to reward frequently used assets.
- Cost: The resource's EncodedSize is factored into its value.

When the cache exceeds its size budget, it first removes any resources
that have passed their maximum lifetime. Then, it sorts the remaining
resources by this calculated value and evicts the lowest-value items
until the memory target is met.

Bug: 432275223

Change-Id: Ie9796cdb67de7b3b1f531dbabec10ae0170120ff
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6671317
Reviewed-by: Olivier Li <olivierli@chromium.org>
Commit-Queue: Alex Attar <aattar@google.com>
Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1490788}