Add a proper license to webgpu.h's template.

This avoids linter checks to trigger when importing updates of Dawn into
Google3.

Bug:
Change-Id: Ib038d8937cc6c294823b56d52b6f2c5e5e24ffac
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/15140
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>

generator/generator_lib.py

@@ -117,6 +117,11 @@ class _PreprocessingLoader(jinja2.BaseLoader):
         result = []
         indentation_level = 0
 
+        # Filter lines that are pure comments. line_comment_prefix is not enough because it removes
+        # the comment but doesn't completely remove the line, resulting in more verbose output.
+        lines = filter(lambda line: not line.strip().startswith('//*'), lines)
+
+        # Remove indentation templates have for the Jinja control flow.
         for line in lines:
             # The capture in the regex adds one element per block start or end so we divide by two
             # there is also an extra line chunk corresponding to the line end, so we substract it.