Avoid unnecessary allocations in single-file app bundle launch

[elinor-fung]

Remove a bunch of unnecessary transient allocations during single-file launch. The amount scales with the number of bundled assets.

For single-file, self-contained, empty console app, Windows x64:

	Before	After	Delta
Startup time	81.033 ms	79.007 ms	-2.026 ms (-2.50%)
Native heap allocation count	36,318	15,585	-20,733 (-57.09%)
Native heap allocated bytes	11,022.17 KB	9,589.94 KB	-1,432.23 KB (-12.99%)

Startup was using the dotnet/performance repo's TimeToMain scenario - average over 10 runs of 20 launches per run, with every run showing an improvement between 1.3-4.8%. Native heap allocation count and bytes were measured with xperf heap tracing.

cc @dotnet/appmodel @AaronRobinsonMSFT

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[Copilot]

Pull request overview

This PR reduces transient native allocations during single-file app startup by avoiding construction of unused on-disk paths for bundle-contained (non-extracted) assets, and by tightening related probing/control flow in hostpolicy.

Changes:

• Avoid building/reserving full file-system paths when a deps asset is satisfied directly from the single-file bundle (no extraction).
• Simplify probe result handling for “found in bundle” cases to avoid unnecessary path usage/logging.
• Reduce copying in bundle manifest accessors (return relative_path() by reference).

Show a summary per file

File	Description
src/native/corehost/hostpolicy/deps_resolver.cpp	Returns bundled earlier to avoid using an empty candidate path and to streamline probing flow.
src/native/corehost/hostpolicy/deps_entry.cpp	Defers candidate.reserve()/path construction until after bundle probing; updates tracing for extracted vs non-extracted bundle assets.
src/native/corehost/bundle/runner.h	Updates locate() documentation (and should further clarify semantics when not extracted).
src/native/corehost/bundle/runner.cpp	Avoids constructing a “fake” on-disk path for non-extracted bundle entries.
src/native/corehost/bundle/file_entry.h	Returns relative_path() by const reference to avoid copies.

Review details

• Files reviewed: 5/5 changed files
• Comments generated: 1
• Review effort level: Lite

[Copilot]

Review details

Suppressed comments (1)

src/native/corehost/bundle/runner.h:40

• runner_t::locate(const pal::string_t&, pal::string_t&) calls a 3-parameter locate overload which is not declared in runner.h (only defined in runner.cpp). This will not compile, and the preceding comment refers to an extracted_to_disk out-parameter that doesn’t exist on this overload.

        bool locate(const pal::string_t& relative_path, pal::string_t& full_path) const
        {
            bool extracted_to_disk;
            return locate(relative_path, full_path, extracted_to_disk);
        }

• Files reviewed: 5/5 changed files
• Comments generated: 0 new
• Review effort level: Lite

[Copilot]

Review details

• Files reviewed: 6/6 changed files
• Comments generated: 0 new
• Review effort level: Lite

[elinor-fung]

/ba-g build analysis misclassifying known test failures - dotnet/arcade#17340