Rework memory_attributes_table to remove the MEMORY_ATTRIBUTES_TABLE static

[joschock]

Description

Remove MEMORY_ATTRIBUTES_TABLE global static - the pointer in question is stored in the global configuration table. Instead of keeping a duplicate copy, use the entry in the global table.

• adjust core_install_configuration_table return value to include the old pointer if the table is removed or modified.
• add get_configuration_table API to return a pointer from the configuration table for the given vendor guid.
• rework MAT logic to use the config table exclusively.
• Replace POST_RTB atomic bool with Once and add a TestOnce capability for test support to allow resetting the Once for testing purposes.

• Impacts functionality?
• Impacts security?
• Breaking change?
• Includes tests?
• Includes documentation?

How This Was Tested

Passes unit tests; booted on AARCH64 HW, checked MAT table as dumped in UEFI logs.

Integration Instructions

N/A

[codecov]

Codecov Report

❌ Patch coverage is 87.35632% with 11 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
..._core/src/config_tables/memory_attributes_table.rs	73.33%	8 Missing ⚠️
patina_dxe_core/src/config_tables.rs	96.43%	2 Missing ⚠️
patina_dxe_core/src/allocator.rs	0.00%	1 Missing ⚠️

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