Allow sorting TOML table keys

[orf]

Quite often you want to keep the overall structure of a TOML file, but sort the keys within. For example, a Cargo.toml file:

[package]
name = "xyz"

[dependencies]
tokio = {version = "1.38.0", features = ["full"]}
clap = {version = "4.5.4", features = ["derive", "env"]}

Right now this will be re-formatted as

[dependencies]
clap = {version = "4.5.4", features = ["derive", "env"]}
tokio = {version = "1.38.0", features = ["full"]}

[package]
name = "xyz"

Which is annoying - I'd like to keep the [package] table at the top, but just sort the keys (dependencies, mostly) within:

[package]
name = "xyz"

[dependencies]
clap = {version = "4.5.4", features = ["derive", "env"]}
tokio = {version = "1.38.0", features = ["full"]}

This MR adds a flag to support this.

[thclark]

Would love to see this merged! Usually there's only one you want at the top; typically [package] (rust) or [project] (for pyproject.toml) that by convention you want to have access to right at the top of the file.