September infra rollout - continued CoreCLR / Mono test cleanup (minimal) (#40345)

September infra rollout - continued CoreCLR / Mono test cleanup (minimal) (#40345)

Similar to the previous occasion, I have identified this set as the minimum meaningful set of scripts to move without causing too much disruption apart from purely mechanical renames. This change moves the developer-facing test-related CoreCLR scripts under the src/tests folder in accordance with the previous move of the tests themselves:

src/coreclr/build-test.cmd to src/tests/build.cmd
src/coreclr/build-test.sh to src/tests/build.sh
src/coreclr/tests/build.proj to src/tests/build.proj
src/coreclr/tests/runtest.cmd to src/tests/run.cmd
src/coreclr/tests/runtest.sh to src/tests/run.sh
src/coreclr/tests/src/runtest.proj to src/tests/run.proj
src/coreclr/tests/issues.targets to src/tests/issues.targets

The rest of the change constitutes mere path adjustments to match the primary rename.

Fixes: https://github.com/dotnet/runtime/issues/38919

Thanks

Tomas