[New] nvm.sh: add basic support for loongarch64 architecture

[elysia-best]

Like riscv64, LoongArch64 is also an experimental architecture on the Node platform list. Users can install Node.js from the unofficial builds website. However, the uname -m output for the LoongArch64 platform (i.e. loongarch64) differs from the identifier chosen by Node (i.e. loong64). Given that loong64 is an abbreviation of loongarch64. This PR adds the necessary mapping for this.

The following information may be useful:

• The output of uname -m on a LoongArch64 machine running Debian:

  elysia@elysia-loongson:~ (master =)$ uname -m
  loongarch64
  

• Platform list of Node.js: https://github.com/nodejs/node/blob/main/BUILDING.md#platform-list

• An example link on the unofficial build website: https://unofficial-builds.nodejs.org/download/release/v20.5.0/

• Relationship between loongarch64 and loong64: https://areweloongyet.com/en/docs/loong-or-loongarch/