eth/filter, ethclient/gethclient: added fullTx-flag to NewPendingTransactions

[diwu1989]

Porting https://github.com/ethereum/go-ethereum/pull/25186/files to Celo. There were some trivial merge conflicts in eth/filters/api.go that needed to be resolved before this could apply.

Would like this to be merged in and deployed to Forno so that websocket streams from the pub RPC TX pool includes the body, otherwise, there's just extra load doing round trip to fetch via pending tx header.

[codecov[bot]]

Codecov Report

Attention: 11 lines in your changes are missing coverage. Please review.

Comparison is base (755b653) 55.06% compared to head (776aed1) 55.17%. Report is 5 commits behind head on master.

Files	Patch %	Lines
eth/filters/api.go	42.10%	11 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2239 +/- ## ========================================== + Coverage 55.06% 55.17% +0.10% ========================================== Files 683 683 Lines 114533 114538 +5 ========================================== + Hits 63073 63191 +118 + Misses 47562 47468 -94 + Partials 3898 3879 -19 ```

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[github-actions[bot]]

Coverage from tests in ./e2e_test/... for ./consensus/istanbul/... at commit 69dbdae732d3c3d62ee5678c2d93096f7d43cb7a

coverage: 50.9% of statements across all listed packages

coverage:  63.2% of statements in consensus/istanbul
coverage:  42.8% of statements in consensus/istanbul/announce
coverage:  56.0% of statements in consensus/istanbul/backend
coverage:   0.0% of statements in consensus/istanbul/backend/backendtest
coverage:  24.3% of statements in consensus/istanbul/backend/internal/replica
coverage:  65.1% of statements in consensus/istanbul/core
coverage:  50.0% of statements in consensus/istanbul/db
coverage:   0.0% of statements in consensus/istanbul/proxy
coverage:  64.2% of statements in consensus/istanbul/uptime
coverage:  51.8% of statements in consensus/istanbul/validator
coverage:  79.2% of statements in consensus/istanbul/validator/random

[github-actions[bot]]

[diwu1989]

Thanks for the merge, there's a followup bug fix in https://github.com/ethereum/go-ethereum/pull/26126 that I'll also port over so that the pending RPC transaction JSON is consistent across the different APIs.