[RISCV] Add support of Sdext,Sdtrig extentions (#120936)

`Sdext` and `Sdtrig` are RISC-V extensions related to debugging.

The full specification can be found at

https://github.com/riscv/riscv-

[RISCV] Add support of Sdext,Sdtrig extentions (#120936)

`Sdext` and `Sdtrig` are RISC-V extensions related to debugging.

The full specification can be found at

https://github.com/riscv/riscv-debug-spec/releases/download/1.0.0-rc4/riscv-debug-specification.pdf

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[NFC] [RISCV] Refactor class RISCVExtension (#120040)

I think typo can be avoided by reducing the number of times we re-enter
the extension name.