Avoid shared-file races in parallel CoreCLR builds

[EgorBo]

When I build multiple dotnet/runtime repos on the same windows machine at the same time I quite often run into build failures.

Avoid cross-checkout file contention in Windows CoreCLR builds:

• capture Python discovery output without %TEMP%\pythonlocation.txt
• copy MSVC PGO databases into each build tree before linking

Validated with a Release clr.runtime build and two concurrent isolated Release JIT builds.

Addresses #45423 and #46018.

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Pull request overview

This PR reduces cross-checkout build contention on Windows by removing shared-temp-file usage during Python discovery and by making PGO database inputs build-local to avoid sharing violations during concurrent CoreCLR builds.

Changes:

• Replace %TEMP%\pythonlocation.txt-based Python discovery in run.cmd and build-runtime.cmd with in-process capture via for /f.
• Update CoreCLR PGO support to copy MSVC PGO database files into the build tree before linking, avoiding shared-file access across parallel builds.

File summaries

File	Description
src/tests/run.cmd	Avoids writing a shared temp file when discovering Python for test runs.
src/coreclr/build-runtime.cmd	Avoids writing a shared temp file when discovering Python for CoreCLR builds.
src/coreclr/pgosupport.cmake	Copies PGO database inputs into the build output tree to avoid Windows sharing violations during linking.

Review details

• Files reviewed: 3/3 changed files
• Comments generated: 2
• Review effort level: Lite