Fix #5833: notification of fxa state change updates app menu badge

[garvankeeley]

post a notification .FirefoxAccountStateChange when the FirefoxAccount.stateCache is changed

[mozillamobilebot]

SwiftLint found issues

Warnings

File	Line	Reason
FirefoxAccount.swift	53	Colons should be next to the identifier when specifying a type and next to the key in dictionary literals. (colon)
FirefoxAccount.swift	338	Colons should be next to the identifier when specifying a type and next to the key in dictionary literals. (colon)
FirefoxAccount.swift	41	Prefer empty collection over optional collection. (discouraged_optional_collection)
FirefoxAccount.swift	76	Prefer empty collection over optional collection. (discouraged_optional_collection)
FirefoxAccount.swift	80	Prefer empty collection over optional collection. (discouraged_optional_collection)
FirefoxAccount.swift	125	Prefer empty collection over optional collection. (discouraged_optional_collection)
BrowserViewController.swift	455	if, for, guard, switch, while, and catch statements shouldn't unnecessarily wrap their conditionals or arguments in parentheses. (control_statement)
BrowserViewController.swift	1149	if, for, guard, switch, while, and catch statements shouldn't unnecessarily wrap their conditionals or arguments in parentheses. (control_statement)
BrowserViewController.swift	495	Prefer empty collection over optional collection. (discouraged_optional_collection)
BrowserViewController.swift	886	Prefer empty collection over optional collection. (discouraged_optional_collection)
BrowserViewController.swift	1387	Prefer empty collection over optional collection. (discouraged_optional_collection)
BrowserViewController.swift	2523	Force casts should be avoided. (force_cast)
BrowserViewController.swift	46	Variables should not have redundant type annotation (redundant_type_annotation)
BrowserViewController.swift	2126	Variables should not have redundant type annotation (redundant_type_annotation)

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