Support eth_signTransaction and eth_sendRawTransaction

[yrliou]

This issue is to add support of eth_signTransaction provider API, see eth_signTransaction at https://ethereum.github.io/execution-apis/api-documentation/.
Just for reference, https://web3js.readthedocs.io/en/v1.2.11/web3-eth.html#signtransaction for interface defined by web3.js.

Testing app provided by mistx:
https://github.com/juice0x/test-mistx-transaction-app
In this repo there's a test for signing an eth:usdc swap with signTransaction as well as a sample app to test in the browser environment. the code in the test is an example of working code however it will fail due to the mock provider not supporting signTransaction. it should succeed with a provider that supports it.

cc @bbondy

[srirambv]

Verification passed on

Brave	1.48.151 Chromium: 109.0.5414.119 (Official Build) beta (64-bit)
Revision	772095164c7d5d4e73160f858efed3b5e87eca83-refs/branch-heads/5414@{#1458}
OS	Windows 11 Version 22H2 (Build 22621.755)

• Verified steps from brave/brave-core#16247
• Verified signed transaction changes to confirmed when eth_sendRawTransaction goes through
• Verified one of the signed transaction drops when there are two of them and one of them gets confirmed
• Encountered #28205

Normal Flow	Nonce drop
23582-Normal.Flow.mp4	23582-Nonce.Drop.mp4

[srirambv]

Removing OS/Android label as there is an Android specific issue that is logged #28363