DevTools: Report missing description and placeholder example as localizability violation in presubmit

This patch adds a localizability check to the presubmit script that reports
errors for empty descriptions, after https://crrev.com/c/1688716 adds auto-
generated descriptions.

Example error messages:

third_party/blink/renderer/devtools/front_end/accessibility/accessibility_strings.grdp
Line 36: missing description for message with the name "IDS_DEVTOOLS_185551542d4a950d6ed4a90e0875dfde"
third_party/blink/renderer/devtools/front_end/animation/animation_strings.grdp Line 10:
missing <ex> in <ph> tag with the name "BUTTON_TEXTCONTENT"

This patch also improves error reporting by changing full file path to partial
path from src/ so that it's more consistent with the presubmit error style.

Note: there may be new strings added without a description and/or placeholder
example while this patch is on review. In that case I will fix them so the
check can be enabled without any problem.

Bug: 941561
Change-Id: If609d234b67acb76dfd9c66e2f8880d9875034cc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1693028
Commit-Queue: Mandy Chen <mandy.chen@microsoft.com>
Reviewed-by: Joel Einbinder <einbinder@chromium.org>
Cr-Commit-Position: refs/heads/master@{#681975}