[llvm] [Support][YamlTraits] Add quoting for keys in textual YAML representation (PR #88763)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> One affected case is output of control registers in AMDGPU Msgpack metadata, which are printed in a format like this:
> 
> ```
>    0x2cca (SPI_SHADER_PGM_RSRC1_ES): 42
> ```
> 
> With this patch, the key is quoted:
> 
> ```
>    '0x2cca (SPI_SHADER_PGM_RSRC1_ES)': 42
> ```

Could we just drop the space in the printing here? 

https://github.com/llvm/llvm-project/pull/88763