tools,icu: read full ICU version info from file

* ATM on every ICU version bump we need to update these data. Reading
  it from a file makes it independant of `configre.py` changes.
* Update guide.

PR-URL: #23269
Refs: #23245
Reviewed-By: Steven R Loomis <srloomis@us.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

configure.py

@@ -1,3 +1,4 @@
+import json
 import sys
 import errno
 import optparse
@@ -1252,13 +1253,9 @@ def glob_to_var(dir_base, dir_sub, patch_dir):
   return list
 
 def configure_intl(o):
-  icus = [
-    {
-      'url': 'https://sourceforge.net/projects/icu/files/ICU4C/62.1/icu4c-62_1-src.zip',
-      'md5': '408854f7b9b58311b68fab4b4dfc80be',
-    },
-  ]
   def icu_download(path):
+    with open('tools/icu/current_ver.dep') as f:
+      icus = json.load(f)
     # download ICU, if needed
     if not os.access(options.download_path, os.W_OK):
       error('''Cannot write to desired download path.

tools/icu/README.md

@@ -92,9 +92,9 @@ make clean
 tools/license-builder.sh
 ```
 
-- Now, fix the default URL for the `full-icu` build in `/configure.py`, in
-the `configure_intl()` function. It should match the ICU URL used in the
-first step.  When this is done, the following should build with full ICU.
+- Update the URL and hash for the full ICU file in `tools/icu/current_ver.dep`.
+It should match the ICU URL used in the first step.  When this is done, the
+following should build with full ICU.
 
 ```shell
 # clean up
@@ -104,7 +104,7 @@ make
 make test-ci
 ```
 
-- commit the change to `configure.py` along with the updated `LICENSE` file.
+- commit the change to `tools/icu/current_ver.dep` and `LICENSE` files.
 
   - Note: To simplify review, I often will “pre-land” this patch, meaning that
   I run the patch through `curl -L https://github.com/nodejs/node/pull/xxx.patch

tools/icu/current_ver.dep

@@ -0,0 +1,6 @@
+[
+  {
+    "url": "https://sourceforge.net/projects/icu/files/ICU4C/62.1/icu4c-62_1-src.zip",
+    "md5": "408854f7b9b58311b68fab4b4dfc80be"
+  }
+]