Declass encoder/decoder for reduced size

[tnorling]

• Moves Base64Encoder and Base64Decoder into functions rather than class methods
• Updates their implementations to use built-in browser APIs (now available since we don't support IE anymore!)

[codecov-commenter]

Codecov Report

Merging #6416 (163ba8e) into dev (81d34b4) will increase coverage by 1.37%.
Report is 286 commits behind head on dev.
The diff coverage is n/a.

Flag	Coverage Δ
msal-angular	96.73% <ø> (+0.22%)	⬆️
msal-browser	85.16% <ø> (-1.31%)	⬇️
msal-common	?
msal-core	?
msal-node	?
msal-node-extensions	?
msal-react	94.24% <ø> (-0.45%)	⬇️
node-token-validation	?

Files Changed	Coverage Δ
lib/msal-angular/src/constants.ts	100.00% <ø> (ø)
lib/msal-angular/src/msal.broadcast.service.ts	100.00% <ø> (ø)
lib/msal-angular/src/msal.guard.ts	90.78% <ø> (+0.64%)	⬆️
lib/msal-angular/src/msal.interceptor.ts	100.00% <ø> (ø)
lib/msal-angular/src/msal.module.ts	100.00% <ø> (ø)
lib/msal-angular/src/msal.navigation.client.ts	93.33% <ø> (+0.47%)	⬆️
lib/msal-angular/src/msal.redirect.component.ts	100.00% <ø> (ø)
lib/msal-angular/src/msal.service.ts	100.00% <ø> (ø)
lib/msal-angular/src/packageMetadata.ts	100.00% <ø> (ø)
...b/msal-browser/src/app/IPublicClientApplication.ts	41.17% <ø> (-2.58%)	⬇️
... and 42 more

... and 180 files with indirect coverage changes