perf(discovery): support caching discovery in one build pass

[innocenzi]

This pull request adds support for caching Discovery with only one build pass.

It's not a big deal that this is not the case, because we don't care about discovery:generate performance, however since it does load the files it go through, some files can be loaded twice during the lifespan of the application, and that may cause issues (such as with files declaring functions without verifying if they exist before).

So this work by allowing (new BootDiscovery)() to return the list of discoveries, and allowing (new GenerateDiscoveryCache)() to receive a list of discoveries, in which case it skips building it again.

[github-actions]

Benchmark Results

Comparison of feat/get-discoveries against 3.x (f1162475c1a432bec8d9c8442f46f7c895db7765).

Open to see the benchmark results

Benchmark	Set	Mem. Peak	Time	Variability
ViewRenderBench(benchPlainHtml)	-	21.956mb 0.00%	481.587μs -9.52%	±1.74% -35.31%

_{Generated by phpbench against commit de35a86}