[credentialless] Fix WPT interactions.

When run with the official WPT test runner, the COEP credentialless are
failing pretty often compared to Chrome's test runner:
https://wpt.fyi/results/html/cross-origin-embedder-policy/credentialless?label=experimental
The reason is that test aren't run in isolation. Cookies added for one
test are kept for the next one. This shouldn't be a problem for COEP
credentialless, because every test use a different key.

However, there was a problem parsing the cookie value. Chrome insert
spaces and new lines in the cookie value.

Previously:
```
coep_credentialless_script=xxx;
coep_credentialless_link=yyy
```
was parsed as:
```
{
  "coep_credentialess_script": "xxx",
  " coep_credentialless_link": "yyy",
}
```
causing the test to fail when run in sequence.

Solution was to properly trim the values, to remove extra spaces.

Fixed: 1254649
Bug: 1254649
Change-Id: Ic0d51c5b6a8422a8a1f3a9348a54d707f71f7b02
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3208052
Reviewed-by: Antonio Sartori <antoniosartori@chromium.org>
Commit-Queue: Arthur Sonzogni <arthursonzogni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#928649}
diff --git a/html/cross-origin-embedder-policy/credentialless/resources/common.js b/html/cross-origin-embedder-policy/credentialless/resources/common.js
index 85e539a..ce21c76 100644
--- a/html/cross-origin-embedder-policy/credentialless/resources/common.js
+++ b/html/cross-origin-embedder-policy/credentialless/resources/common.js
@@ -61,7 +61,7 @@
     .split(';')
     .map(v => v.split('='))
     .reduce((acc, v) => {
-      acc[v[0]] = v[1];
+      acc[v[0].trim()] = v[1].trim();
       return acc;
     }, {});
 }