BaseTools/Plugin/HostBasedUnitTestRunner: Merge clang coverage files

[cosmolai]

Description

For clang build it doesn't generate coverage file in Build folder. This change is to generate coverage file for all modules.

• Breaking change?
  • Breaking change - Does this PR cause a break in build or boot behavior?
  • Examples: Does it add a new library class or move a module to a different repo.
• Impacts security?
  • Security - Does this PR have a direct security impact?
  • Examples: Crypto algorithm change or buffer overflow fix.
• Includes tests?
  • Tests - Does this PR include any explicit test code?
  • Examples: Unit tests or integration tests.

How This Was Tested

Use stuart commands to run unit test and generate coverage file.
example:
cd workspace

python3 -m venv venv313
. ./venv313/bin/activate
pip install --upgrade -r ./Edk2/pip-requirements.txt
python3 ./Edk2/BaseTools/Edk2ToolsBuild.py -t GCC5
stuart_setup -c ./X/.pytool/CISettings.py -a X64 TOOL_CHAIN_TAG=CLANGDWARF
stuart_update -c ./X/.pytool/CISettings.py -a X64 TOOL_CHAIN_TAG=CLANGDWARF
stuart_ci_build -c ./X/.pytool/CISettings.py -a X64 -t NOOPT TOOL_CHAIN_TAG=CLANGDWARF
deactivate

check if Build/coverage.xml is generated.

Integration Instructions

NA