Update to Babel 8

[nicolo-ribaudo]

I diffed the Babel 7 and Babel 8 builds for generic, mozcentral, and lib. They are almost identical.

• There re no differences in mozcentral
• Both in generic and lib, when we inline the .ftl strings in

  pdf.js/web/genericl10n.js

  Lines 135 to 141 in 7e7ed1b

  	const text =
  	typeof PDFJSDev === "undefined"
  	? await fetchData(
  	new URL("../l10n/en-US/viewer.ftl", window.location.href),
  	/* type = */ "text"
  	)
  	: PDFJSDev.eval("DEFAULT_FTL");

  , Babel 8 emits non-ASCII characters by default rather than forcefully escaping them (e.g. Babel 8 preserves ’, while Babel 7 converts it to \u2019).

I had to inline the Babel plugin that injects the header comment in the lib build, as it didn't support Babel 7. I opened a PR (Shopify/babel-plugin-add-header-comment#9), but it's so simple that it's probably not worth waiting.

The inlined plugin also keeps the copyright notice, which I believe should be there while it wasn't there before:

  -/**
  -* 
  -* Licensed under the Apache License, Version 2.0 (the "License");
  -* you may not use this file except in compliance with the License.
  -* You may obtain a copy of the License at
  -* 
  -*     http://www.apache.org/licenses/LICENSE-2.0
  -* 
  -* Unless required by applicable law or agreed to in writing, software
  -* distributed under the License is distributed on an "AS IS" BASIS,
  -* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  -* See the License for the specific language governing permissions and
  -* limitations under the License.
  -**/
  +/* Copyright 2024 Mozilla Foundation
  + *
  + * Licensed under the Apache License, Version 2.0 (the "License");
  + * you may not use this file except in compliance with the License.
  + * You may obtain a copy of the License at
  + *
  + *     http://www.apache.org/licenses/LICENSE-2.0
  + *
  + * Unless required by applicable law or agreed to in writing, software
  + * distributed under the License is distributed on an "AS IS" BASIS,
  + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  + * See the License for the specific language governing permissions and
  + * limitations under the License.
  + */

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.81%. Comparing base (59df671) to head (7a2f349).

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #21475   +/-   ##
=======================================
  Coverage   89.80%   89.81%           
=======================================
  Files         260      260           
  Lines       66075    66075           
=======================================
+ Hits        59339    59342    +3     
+ Misses       6736     6733    -3     

Flag	Coverage Δ
browsertest	66.89% <ø> (-0.01%)	⬇️
fonttest	9.02% <ø> (ø)
integrationtest	68.91% <ø> (+0.01%)	⬆️
unittest	57.26% <ø> (+0.01%)	⬆️
unittestcli	56.22% <ø> (+0.01%)	⬆️

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