Put local dependencies in crates directory

With an increasing number of local dependencies, the repo root is getting
somewhat bloated. This commit moves the two current local dependencies into the
newly created `crates` directory, with the intention of using it for all future
local dependencies as well.

Some dependencies which are introduced by currently in-progress pull requests
will need modifications in order for relative paths to work correctly.

crates/printf/Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+name = "fish-printf"
+edition.workspace = true
+rust-version.workspace = true
+version = "0.2.1"
+repository.workspace = true
+description = "printf implementation, based on musl"
+license = "MIT"
+
+[dependencies]
+libc = "0.2.155"
+widestring = { version = "1.0.2", optional = true }
+unicode-segmentation = "1.12.0"
+unicode-width = "0.2.0"
+
+[lints]
+workspace = true