theme_importer: Support importing themes containing comments (#3298)

This PR updates the `theme_importer` with support for parsing theme
files containing comments.

Up until now we've been manually removing comments from the VS Code
theme files.

Release Notes:

- N/A

Cargo.lock

@@ -4433,6 +4433,12 @@ dependencies = [
  "wasm-bindgen",
 ]
 
+[[package]]
+name = "json_comments"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9dbbfed4e59ba9750e15ba154fdfd9329cee16ff3df539c2666b70f58cc32105"
+
 [[package]]
 name = "jwt"
 version = "0.16.0"
@@ -9156,6 +9162,7 @@ dependencies = [
  "convert_case 0.6.0",
  "gpui2",
  "indexmap 1.9.3",
+ "json_comments",
  "log",
  "rust-embed",
  "serde",