build: support substituting/stamping files other than package.json

Similart to `pkg_npm` from `rules_nodejs`, we should have a way to make
use of the stamp constants/placeholders throughout individual package
files. This is not possible at all with `rules_js`'s `npm_package` rule,
nor does it support stamp substitutions out of the box at all.

We have our own `expand_template` machinery to substitute `package.json`
files of npm archives, but we need to expand this to support arbitrary
files inside a package. This will be opt-in for explicitly listed files;
which is a good compromise for simplicity of supporting this.

This commit adds the necessary functionality and demonstrates the
feature by fixing `@angular/build`.

packages/angular/build/BUILD.bazel

@@ -229,6 +229,10 @@ npm_package(
     pkg_deps = [
         "//packages/angular_devkit/architect:package.json",
     ],
+    stamp_files = [
+        "src/tools/esbuild/utils.js",
+        "src/utils/normalize-cache.js",
+    ],
     tags = ["release-package"],
     deps = RUNTIME_ASSETS + [
         ":README.md",

packages/angular/cli/BUILD.bazel

@@ -170,6 +170,9 @@ npm_package(
         "//packages/angular_devkit/schematics:package.json",
         "//packages/schematics/angular:package.json",
     ],
+    stamp_files = [
+        "src/utilities/version.js",
+    ],
     tags = ["release-package"],
     deps = RUNTIME_ASSETS + [
         ":README.md",

tools/bazel/npm_package.bzl

@@ -13,6 +13,7 @@ def npm_package(
         deps = [],
         visibility = None,
         pkg_deps = [],
+        stamp_files = [],
         pkg_json = "package.json",
         **kwargs):
     if name != "pkg":
@@ -74,11 +75,23 @@ def npm_package(
         stamp_substitutions = get_npm_package_substitutions_for_rjs(),
     )
 
+    stamp_targets = []
+    for f in stamp_files:
+        expand_template(
+            name = "stamp_file_%s" % f,
+            template = f,
+            out = "substituted/%s" % f,
+            substitutions = NO_STAMP_PACKAGE_SUBSTITUTIONS,
+            stamp_substitutions = get_npm_package_substitutions_for_rjs(),
+        )
+
+        stamp_targets.append("stamp_file_%s" % f)
+
     _npm_package(
         name = "npm_package",
         visibility = visibility,
         # Note: Order matters here! Last file takes precedence after replaced prefixes.
-        srcs = deps + [":final_package_json"],
+        srcs = deps + stamp_targets + [":final_package_json"],
         replace_prefixes = {
             "substituted_final/": "",
             "substituted_with_tars/": "",