[msal-browser] Fix encoding issues

[pkanher617]

This PR fixes a couple issues

• Cookies were not encoded before being saved, which resulted in cookie key:value errors when setting b64 values with trailing = characters.
• State was being double encoded in some cases on the server-side, adding an additional decodeURIComponent should fix those issues.

[jmckennon]

Looks good, but if state is (arbitrarily?) being double-encoded on the backend... shouldn't we look to get that fixed rather than double decode as well? Seems odd. What if they end up triple encoding something someday?

[tnorling]

Looks good, but if state is (arbitrarily?) being double-encoded on the backend... shouldn't we look to get that fixed rather than double decode as well? Seems odd. What if they end up triple encoding something someday?

Agree with this. Should we maybe check for a certain property to know we're done decoding?

[jasonnutter]

Looks good, but if state is (arbitrarily?) being double-encoded on the backend... shouldn't we look to get that fixed rather than double decode as well? Seems odd. What if they end up triple encoding something someday?

Yes, we should get this fixed on the server, but for now, I think it is fine to assume things will at most be encoded twice.

[coveralls]

Coverage decreased (-0.06%) to 79.218% when pulling 3b880f3 on fix-url-encoding-msal-browser into 532a9a4 on dev.