DevTools: Create a grdp file for shared strings to avoid confusion

Since the current localization system uses a unique ID for each string that
is calculated based on the the md5 hash of the string, each string
in the grdp files needs to be unique. However, there are strings in the
frontend that appear multiple times. When such strings are moved across
folders, sometimes a seemingly random grdp file is changed by the autofix
script. (See https://crrev.com/c/1683826 for an example)

This CL introduces shared_strings.grdp, a file dedicated for strings that
are shared across folders/grdp files. Instead of putting these strings in
the grdp files that come first when sorted alphabetically, they live in
shared_strings.grdp and have common descriptions among all instances of
such strings. This way if shared strings need to be moved, it's more clear
what's going on.

Note that this CL contains a lot of changes that are generated automatically
(e.g. shared strings are removed from their current locations), so here's
the list of actual changes that need to be reviewed:

* shared_strings.grdp file is added to front_end/langpacks and front_end/langpacks/
devtools_ui_strings.grd
* path to shared_strings.grdp is added to scripts/localization_utils/localization_utils.js
* in scripts/localization_utils/check_localized_strings.js, the parser marks
strings that appear more than once as shared and set the target grdp file to be
shared_strings.grdp
* shared_strings.grdp file is checked by scripts/check_localizability.js for
localizability violations
* shared_strings.grdp messages have common descriptions added

Bug: 941561
Change-Id: I00db23854656509f2f03988e70adc0109b6e09d6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1800918
Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Mandy Chen <mandy.chen@microsoft.com>
Cr-Original-Commit-Position: refs/heads/master@{#697667}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: d10bf7c5a97cf9184866c1117935c199bacf7ff3
diff --git a/scripts/check_localizability.js b/scripts/check_localizability.js
index 91e7158..98e695c 100644
--- a/scripts/check_localizability.js
+++ b/scripts/check_localizability.js
@@ -49,6 +49,7 @@
       filePaths = process.argv.slice(2);
     await Promise.all(filePathPromises);
 
+    filePaths.push(localizationUtils.SHARED_STRINGS_PATH);
     const auditFilePromises = filePaths.map(filePath => auditFileForLocalizability(filePath, errors));
     await Promise.all(auditFilePromises);
   } catch (err) {