Reduced dependencies and copied signer from aws-amplify

[cgalvan]

Issue #, if available:

Fixes #29

Description of changes:

The purpose of this change was to reduce the size of our dependencies. In #29 it was uncovered that our total dependency size was ~280MB. A lot of this came from @aws-amplify/core, which we were using for our sigv4 signing.

Prior to this change, our dependencies were:

"@aws-amplify/core": "^5.5.0",
"@aws-sdk/client-location": "^3.359.0",
"@aws-sdk/credential-providers": "^3.359.0",
"@aws-sdk/types": "^3.347.0"

I updated these to the latest versions, and there had been a lot of dependency trimming, but there was a major API breakage in @aws-amplify/core. They no longer export the Signer, and are intending to deprecate it in favor of another internal signing library (that the Signer currently calls internally), which is also not exported:

https://github.com/aws-amplify/amplify-js/blob/main/packages/core/src/clients/middleware/signing/signer/signatureV4

So, I have copied over the Signer class and left a long comment detailing this move.

This changes our dependencies to:

"@aws-crypto/sha256-js": "^5.2.0",
"@aws-sdk/client-location": "^3.549.0",
"@aws-sdk/credential-providers": "^3.549.0",
"@aws-sdk/types": "^3.535.0",
"@smithy/util-hex-encoding": "^2.0.0"

Installing these dependencies in an empty repo results in only 19MB!

Testing:

Updated the unit tests to test the output of the signer. Ran unit tests and all pass.

> npm test
 PASS  src/index.test.ts
 PASS  src/cognito/index.test.ts
 PASS  src/apikey/index.test.ts
-------------|---------|----------|---------|---------|-------------------
File         | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
-------------|---------|----------|---------|---------|-------------------
All files    |   97.47 |    69.56 |   94.44 |   98.27 |
 src         |     100 |      100 |     100 |     100 |
  index.ts   |     100 |      100 |     100 |     100 |
 src/apikey  |     100 |      100 |     100 |     100 |
  index.ts   |     100 |      100 |     100 |     100 |
 src/cognito |     100 |      100 |     100 |     100 |
  index.ts   |     100 |      100 |     100 |     100 |
 src/utils   |   96.73 |    58.82 |    92.3 |   97.75 |
  signer.ts  |   96.73 |    58.82 |    92.3 |   97.75 | 321,349
-------------|---------|----------|---------|---------|-------------------

Test Suites: 3 passed, 3 total
Tests:       19 passed, 19 total
Snapshots:   0 total
Time:        0.953 s, estimated 1 s
Ran all test suites.

Also ran npm run build and used the output in a simple local test app with both API key and cognito and verified a map is loaded properly.