set Cargo feature resolver to v2 (#8917)

* fix: version of Cargo feature resolver.

This commit solve the ambiguity to determin the version of resolver.
To get more detail, see the following two documents:

- https://doc.rust-lang.org/cargo/reference/resolver.html#resolver-versions
- https://doc.rust-lang.org/edition-guide/rust-2021/default-cargo-resolver.html

* unified: Rust edition in all workspaces.

Now, the Rust 2021 is available in all workspaces.

* fined up: Cargo.toml by using workspace inheritance.

To get more detail of the `workspace.package` table, see a following document:

- https://doc.rust-lang.org/cargo/reference/workspaces.html#the-package-table

Cargo.toml

@@ -1,4 +1,5 @@
 [workspace]
+resolver = "2"
 members = [
   "helix-core",
   "helix-view",
@@ -37,3 +38,8 @@ package.helix-term.opt-level = 2
 [workspace.dependencies]
 tree-sitter = { version = "0.20", git = "https://github.com/tree-sitter/tree-sitter", rev = "ab09ae20d640711174b8da8a654f6b3dec93da1a" }
 nucleo = "0.2.0"
+
+[workspace.package]
+edition = "2021"
+license = "MPL-2.0"
+rust-version = "1.70"