Rtree from displaylist

[flar]

Fixes flutter/flutter#108083

This PR simply adds a new rtree() method on DisplayList that will return an RTree implementation representing its contents, primarily for use in PlatformView embedders. No other optimizations are added that leverage the RTree.

[flar]

I'll note that I had to make one change to the flow/rtree code when I copied it to DisplayList as it was assuming that the RTree was created with supplementary data (see lines following 22c19):

Diff of rtree.cc against display_list_rtree.cc

5,7c5
< #include "rtree.h"
< 
< #include <list>
---
> #include "flutter/display_list/display_list_rtree.h"
10d7
< #include "third_party/skia/include/core/SkBBHFactory.h"
14c11
< RTree::RTree() : bbh_{SkRTreeFactory{}()}, all_ops_count_(0) {}
---
> DlRTree::DlRTree() : bbh_{SkRTreeFactory{}()}, all_ops_count_(0) {}
16,18c13,15
< void RTree::insert(const SkRect boundsArray[],
<                    const SkBBoxHierarchy::Metadata metadata[],
<                    int N) {
---
> void DlRTree::insert(const SkRect boundsArray[],
>                      const SkBBoxHierarchy::Metadata metadata[],
>                      int N) {
22c19
<     if (metadata != nullptr && metadata[i].isDraw) {
---
>     if (metadata == nullptr || metadata[i].isDraw) {
29c26
< void RTree::insert(const SkRect boundsArray[], int N) {
---
> void DlRTree::insert(const SkRect boundsArray[], int N) {
33c30
< void RTree::search(const SkRect& query, std::vector<int>* results) const {
---
> void DlRTree::search(const SkRect& query, std::vector<int>* results) const {
37c34
< std::list<SkRect> RTree::searchNonOverlappingDrawnRects(
---
> std::list<SkRect> DlRTree::searchNonOverlappingDrawnRects(
84c81
< size_t RTree::bytesUsed() const {
---
> size_t DlRTree::bytesUsed() const {
88,89c85,86
< RTreeFactory::RTreeFactory() {
<   r_tree_ = sk_make_sp<RTree>();
---
> DlRTreeFactory::DlRTreeFactory() {
>   r_tree_ = sk_make_sp<DlRTree>();
92c89
< sk_sp<RTree> RTreeFactory::getInstance() {
---
> sk_sp<DlRTree> DlRTreeFactory::getInstance() {
96c93
< sk_sp<SkBBoxHierarchy> RTreeFactory::operator()() const {
---
> sk_sp<SkBBoxHierarchy> DlRTreeFactory::operator()() const {

[ColdPaleLight]

This PR LGTM once it LGT @chinmaygarde ( except for the misuse of saved_offsets_).

[flar]

Discovered during writing tests for the conditions that @ColdPaleLight identified - we were only applying the saveLayer image filter if there was also a clip to apply. In practice, since we have a default cull rect here, we'll always have a clip to apply anyway.