MdeModulePkg: Localize the mInternalRT global var in RuntimeResetSystemLib

[os-d]

Description

This avoids a name collision with UefiRuntimeLib which causes a linker error if a platform includes both libraries.

• [ ] Impacts functionality?
  • Functionality - Does the change ultimately impact how firmware functions?
  • Examples: Add a new library, publish a new PPI, update an algorithm, ...
• [ ] Impacts security?
  • Security - Does the change have a direct security impact on an application, flow, or firmware?
  • Examples: Crypto algorithm change, buffer overflow fix, parameter validation improvement, ...
• [ ] Breaking change?
  • Breaking change - Will anyone consuming this change experience a break in build or boot behavior?
  • Examples: Add a new library class, move a module to a different repo, call a function in a new library class in a pre-existing module, ...
• [ ] Includes tests?
  • Tests - Does the change include any explicit test code?
  • Examples: Unit tests, integration tests, robot tests, ...
• [ ] Includes documentation?
  • Documentation - Does the change contain explicit documentation additions outside direct code modifications (and comments)?
  • Examples: Update readme file, add feature readme file, link to documentation on an a separate Web page, ...

How This Was Tested

2311 commit.

Integration Instructions

N/A.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Please upload report for BASE (release/202405@1c424c1). Learn more about missing BASE report.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## release/202405 #1027 +/- ## ================================================= Coverage ? 17.80% ================================================= Files ? 107 Lines ? 10236 Branches ? 2105 ================================================= Hits ? 1823 Misses ? 8399 Partials ? 14 ``` | [Flag](https://app.codecov.io/gh/microsoft/mu_basecore/pull/1027/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=microsoft) | Coverage Δ | | |---|---|---| | [MdeModulePkg](https://app.codecov.io/gh/microsoft/mu_basecore/pull/1027/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=microsoft) | `17.80% <ø> (?)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=microsoft#carryforward-flags-in-the-pull-request-comment) to find out more.

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