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

crates/theme_importer/Cargo.toml

@@ -11,6 +11,7 @@ anyhow.workspace = true
 convert_case = "0.6.0"
 gpui = { package = "gpui2", path = "../gpui2" }
 indexmap = "1.6.2"
+json_comments = "0.2.2"
 log.workspace = true
 rust-embed.workspace = true
 serde.workspace = true