Refactor snapshot build (#2825)

Instead of using core/snapshot_creator.rs, instead two crates are
introduced which allow building the snapshot during build.rs.

Rollup is removed and replaced with our own bundler. This removes
the Node build dependency. Modules in //js now use Deno-style imports
with file extensions, rather than Node style extensionless imports.

This improves incremental build time when changes are made to //js files
by about 40 seconds.

1 files changed, 9 insertions, 0 deletions

diff --git a/cli_snapshots/README.md b/cli_snapshots/README.md
new file mode 100644
index 000000000..427429a2b
--- /dev/null
+++ b/cli_snapshots/README.md
@@ -0,0 +1,9 @@
+This is a small crate which exports just a few static blobs. It contains a
+build.rs file which compiles Deno's internal JavaScript and TypeScript code
+first into a single AMD bundle, and then into a binary V8 Snapshot.
+
+The main Deno executable crate ("cli") depends on this crate and has access to
+all the runtime code.
+
+The //js/ directory should be moved as a sub-directory of this crate, to denote
+the dependency structure. However, that is left to future work.