feat(experimentalIdentityAndAuth): Add generic @httpBearerAuth support

[syall]

Issue #, if available:

N/A.

Description of changes:

NOTE: All of these are under the experimentalIdentityAndAuth feature flag

NOTE: Dependent on #881

• Adding config properties token:

  /**
   * The token used to authenticate requests.
   */
  token?: TokenIdentity | TokenIdentityProvider;

• @smithy/experimental-identity-and-auth package: add the TokenIdentity interface and TokenIdentityProvider type (these are still only in @aws-sdk/types currently), and default HttpBearerAuthSigner implementation.
• Add back operations that support @httpBearerAuth in the generic client test

Testing:

• @httpBearerAuth client codegen diff given the following model changes: https://gist.github.com/syall/a595c7738c380176a528ff29016f1c2c#file-httpbearerauth-trait-client-diff

   // feat(experimentalIdentityAndAuth): uncomment operations as individual
   //   auth scheme support is implemented
   // @httpApiKeyAuth(name: "X-Api-Key", in: "header")
  -// @httpBearerAuth
  +@httpBearerAuth
   // @sigv4(name: "weather")
   // @auth([sigv4])
   @paginated(inputToken: "nextToken", outputToken: "nextToken", pageSize: "pageSize")
  @@ -27,11 +27,12 @@ service Weather {
           //   auth scheme support is implemented
           // experimentalIdentityAndAuth
           // OnlyHttpApiKeyAuth
  -        // OnlyHttpBearerAuth
  +        OnlyHttpBearerAuth
           // OnlyHttpApiKeyAndBearerAuth
           // OnlyHttpApiKeyAndBearerAuthReversed
           // OnlyHttpApiKeyAuthOptional
  -        // SameAsService
  +        OnlyHttpBearerAuthOptional
  +        SameAsService
       ]
   }

• No codegen diff for aws-sdk-js-v3

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been committed and included in this pull request. See CONTRIBUTING.md.

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