Start on a database-backed prompt library (#12468)

Using the file system as a database seems like it's easy, but it's
actually a real pain. I'd like to use LMDB to store the prompts locally
so we have more control. We can always add an export option, but I want
the source of truth to be somewhere other than the file system.

So far, I have a PromptStore which is global to the application and can
be initialized on startup. Then there's a `PromptLibrary` which is
intended to be the root of a new kind of Zed window. I haven't actually
seen pixels yet, but I've sketched out the basics needed to create a new
prompt, save, etc.

Still lots to figure out but the foundations of being backed by a DB and
rendering in an independent window are in place.

/cc @iamnbutler @as-cii 

Release Notes:

- N/A

---------

Co-authored-by: Antonio Scandurra <me@as-cii.com>

Cargo.lock

@@ -339,6 +339,7 @@ dependencies = [
  "anthropic",
  "anyhow",
  "assistant_slash_command",
+ "async-watch",
  "cargo_toml",
  "chrono",
  "client",
@@ -347,13 +348,12 @@ dependencies = [
  "ctor",
  "editor",
  "env_logger",
- "feature_flags",
  "file_icons",
  "fs",
  "futures 0.3.28",
  "fuzzy",
  "gpui",
- "gray_matter",
+ "heed",
  "http 0.1.0",
  "indoc",
  "language",
@@ -824,6 +824,15 @@ dependencies = [
  "tungstenite 0.16.0",
 ]
 
+[[package]]
+name = "async-watch"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a078faf4e27c0c6cc0efb20e5da59dcccc04968ebf2801d8e0b2195124cdcdb2"
+dependencies = [
+ "event-listener 2.5.3",
+]
+
 [[package]]
 name = "async_zip"
 version = "0.0.17"
@@ -3393,7 +3402,7 @@ version = "0.5.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "330c60081dcc4c72131f8eb70510f1ac07223e5d4163db481a04a0befcffa412"
 dependencies = [
- "libloading 0.7.4",
+ "libloading 0.8.0",
 ]
 
 [[package]]
@@ -4788,18 +4797,6 @@ dependencies = [
  "syn 1.0.109",
 ]
 
-[[package]]
-name = "gray_matter"
-version = "0.2.7"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7188a951c53316d94711b3d944c28cf79968685d295cbe782494e8811fc75554"
-dependencies = [
- "serde",
- "serde_json",
- "toml 0.5.11",
- "yaml-rust",
-]
-
 [[package]]
 name = "grid"
 version = "0.13.0"
@@ -5954,12 +5951,6 @@ dependencies = [
  "safemem",
 ]
 
-[[package]]
-name = "linked-hash-map"
-version = "0.5.6"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0717cef1bc8b636c6e1c1bbdefc09e6322da8a9321966e8928ef80d20f7f770f"
-
 [[package]]
 name = "linkify"
 version = "0.10.0"
@@ -13079,15 +13070,6 @@ dependencies = [
  "toml 0.8.10",
 ]
 
-[[package]]
-name = "yaml-rust"
-version = "0.4.5"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "56c1936c4cc7a1c9ab21a1ebb602eb942ba868cbd44a99cb7cdc5892335e1c85"
-dependencies = [
- "linked-hash-map",
-]
-
 [[package]]
 name = "yansi"
 version = "0.5.1"