feat: add LLVM & MLIR file icons

[bernborgess]

Description

Add file icon for The LLVM Compiler Infrastructure

• File association is .ll
• Based on usage of LLVM vscode extension
• Svg logo obtained from Simple Icons

Add file icon for MLIR files (Multi-Level IR Compiler Framework)

• The svg file is sourced from https://upload.wikimedia.org/wikipedia/commons/0/0e/MLIR_Logo.svg
• This contribution is combined with the MLIR vscode extension.
• The file association is .mlir (MLIR textual assembly format), .pdll (MLIR PDLL pattern files) and .td (TableGen files)

Contribution Guidelines

• By creating this pull request, I acknowledge that I have read the Contribution Guidelines for this project
• I have read the Code Of Conduct and promise to abide by these rules

[github-actions]

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[bernborgess]

@SayanShankhari are the colors ok?

[SayanShankhari]

@bernborgess, there are a few contradictions with the contribution guidelines.

1. the dragon seems too complex to recognize in low resolution, can you re-use existing icon clone extension
2. the hexagon having M looks good, but it needs to fit the grid (check recently added feat(icon): nginx folder icon #3197
   )
3. usually there should be one color for the motive, unless the organization logo is too strict to change

Thanks for asking me, but please consult with core maintainers like @PKief and @lucas-labs. 😄