The support library contains helpers to parse and emit YAML documents.
In the textual YAML representation, some strings need to be quoted, e.g.
when containing unprintable characters.
We already have such quoting implemented for YAML values.
This patch applies the same quoting to YAML *keys*.
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
```
Most test changes come from this pattern.
