feat(map): add GetOrSet for get value of exist key or set it

[AuZhoomLee]

GetOrSet is like setdefault(key, default=None) in Python for dict , and map.getOrDefault(Object key, V defaultValue) in Java for Map, returns the value of the given key or set the fallback value if not present.

[AuZhoomLee]

Mostly, I used to collect value from another, but not sure has been set already, I will make sure first then to get it,

...
v, ok := kv[k]
if !ok {
    kv[k] = defaults.ConstantValue
}
...

In particular, I read config from environment variables or config file to get info, there will always be a default value to make sure essential value has been set for further using.

[lesichkovm]

Is this not the same as ValueOr ?

https://github.com/samber/lo?tab=readme-ov-file#valueor

[AuZhoomLee]

Is this not the same as ValueOr ?

https://github.com/samber/lo?tab=readme-ov-file#valueor

@lesichkovm not same, ValueOr doesn't effect origin, this one can set default to origin

[lesichkovm]

@AuZhoomLee tahnk you for clarifying. Two points:

1. I can see why this is useful. Its best to make it very clear we do modify the original map, as its kind of hidden. May be better name would help with this.

2. Probably make the name similar to the current ValueOr so that they are alpahbetically ordered next to each other in the documentation, making it easier to be found by devs.

Possible options:

• ValueOrSetDefault
• ValueOrSetIfMissing
• ValueOrSetMissing
• ValueOrCreateMissing