[Task] Replace all instances of `__FUNCTION__` with `__func__`

[makubacki]

edk2 has adopted __func__ instead of __FUNCTION__. This issue tracks updating code in Mu repositories (including MU_CHANGE sections and Mu-specific packages) to do the same.

__FUNCTION__ is a pre-standard extension that gcc and Visual C++ among others support, while __func__ was standardized in C99.

Visual Studio began supporting __func__ in VS 2015.

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It is proposed to make this change in the next stable tag integration to Mu. At this time, that is expected to be the 2511 stable tag integration.

[makubacki]

Assigning to @apop5 per offline discussion.