Add restrictions to allowed extensions for File System Access API

These restrictions apply to showOpenFilePicker and showSaveFilePicker.

Existing restriction:

• Extension must start with "."

New restrictions:

• Allowed code points: [A-Za-z0-9+.]
• Extension length cannot exceed to 16, inclusive of leading "."
• Extension cannot end with "."
• Extension cannot end with "local" or "lnk"

(cherry picked from commit c75c5a1e1d72fc923c82ebcaeacc874c88215eff)

Bug: 1137247, 1140403, 1140410, 1140417, 1140435, 1152327
Change-Id: I593f7ca60e05177402885bd3026add16b3a07d0c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2568534
Reviewed-by: Marijn Kruisselbrink mek@chromium.org
Commit-Queue: Austin Sullivan asully@chromium.org
Cr-Original-Commit-Position: refs/heads/master@{#833695}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2576109
Commit-Queue: Marijn Kruisselbrink mek@chromium.org
Auto-Submit: Austin Sullivan asully@chromium.org
Cr-Commit-Position: refs/branch-heads/4324@{#649}
Cr-Branched-From: c73b5a651d37a6c4d0b8e3262cc4015a5579c6c8-refs/heads/master@{#827102}

Ensure that showSaveFilePicker always shows the extension on Mac.

While not a very strong security boundary, making it possible for
users to know what extension a file will be saved with is a good idea.

This also fixes support for compound extensions with the File System
Access API (i.e. ".tar.gz"). The mac file dialog already had a
workaround if the default path ended in such an extension, but the
same problem occurs if the file type filters include a type with a
compound extension.

(cherry picked from commit 5bf1c6c22201394711a9067d2c970ab9f55555d0)

Bug: 1137247
Change-Id: I492bf36baced3de044b8fed5d57fc7b9b5b64400
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2582842
Reviewed-by: Daniel Cheng dcheng@chromium.org
Reviewed-by: Avi Drissman avi@chromium.org
Commit-Queue: Marijn Kruisselbrink mek@chromium.org
Cr-Original-Commit-Position: refs/heads/master@{#835803}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2597785
Reviewed-by: Marijn Kruisselbrink mek@chromium.org
Cr-Commit-Position: refs/branch-heads/4324@{#1044}
Cr-Branched-From: c73b5a651d37a6c4d0b8e3262cc4015a5579c6c8-refs/heads/master@{#827102}

[FSA] Sanitize descriptions for file types.

This collapses white space, limits the length of descriptions to 64
characters, and on windows strips out '*' characters to ensure the
windows dialog itself will still include the true extension.

This last behavior is triggered by the keep_extension_visible flag
that was added in https://crrev.com/c/2582842 to fix a similar problem
on Mac.

(cherry picked from commit 25f38bb6322c0d93722c1faa3f6b4ea2daf2dc90)

Tested: Verified that the extension is shown in the pickers shown by https://fsa-tests.glitch.me/accepts.html
Bug: 1137247
Change-Id: Ife2344589427dbc1055234026601642113b6a791
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2586958
Commit-Queue: Marijn Kruisselbrink mek@chromium.org
Reviewed-by: Robert Liao robliao@chromium.org
Reviewed-by: Victor Costan pwnall@chromium.org
Cr-Original-Commit-Position: refs/heads/master@{#837391}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2597151
Reviewed-by: Marijn Kruisselbrink mek@chromium.org
Cr-Commit-Position: refs/branch-heads/4324@{#1052}
Cr-Branched-From: c73b5a651d37a6c4d0b8e3262cc4015a5579c6c8-refs/heads/master@{#827102}

Release Notes

Notes: backported the fixes to the save file dialog related CVE-2021-21123, CVE-2021-21129, CVE-2021-21130, CVE-2021-21131, CVE-2021-21141.