Update transaction params validation

[rekmarks]

During review of #9984, we discovered that our transaction validation logic permits transactions without to and data fields. Such transactions seem to force our UI into a bad state. Minimally, a meaningful transaction must have either or both fields, in addition to a from address. See eth_sendTransaction on eth.wiki for details.

This PR ensures that transactions without to and data fields are rejected outright. In addition, it:

• Ensures that all errors thrown by validateTxParams are properly formatted JSON-RPC invalidParams errors.
• Improves the error thrown when txParams is not a plain object.

[metamaskbot]

Builds ready [c21b4e7]

• builds: chrome, firefox, opera
• bundle viz: background, ui, inpage, contentscript, ui-libs, bg-libs, phishing-detect
• dep viz: background
• all artifacts

Page Load Metrics (409 ± 43 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	30	84	57	24	11
		domContentLoaded	314	590	407	90	43
		load	315	592	409	90	43
		domInteractive	314	590	407	90	43

[metamaskbot]

Builds ready [17b96ba]

• builds: chrome, firefox, opera
• bundle viz: background, ui, inpage, contentscript, ui-libs, bg-libs, phishing-detect
• dep viz: background
• all artifacts

Page Load Metrics (432 ± 48 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	31	93	55	23	11
		domContentLoaded	300	583	430	100	48
		load	302	586	432	100	48
		domInteractive	300	582	430	100	48

[metamaskbot]

Builds ready [2224166]

• builds: chrome, firefox, opera
• bundle viz: background, ui, inpage, contentscript, ui-libs, bg-libs, phishing-detect
• dep viz: background
• all artifacts

Page Load Metrics (426 ± 51 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	32	101	67	23	11
		domContentLoaded	317	618	424	105	51
		load	319	620	426	105	51
		domInteractive	317	618	424	105	51

[Gudahtt]

LGTM!