abb6fa728598c4cc8874eae1c3c5e587e36424cd fuzz: Initialize a full TestingSetup where appropriate (Carl Dong)
713314abfa224efceb7ba6fa7fef37c449902936 fuzz: Consolidate fuzzing TestingSetup initialization (Carl Dong)
Pull request description:
```
Previously, the {Basic,}TestingSetup for fuzzers were set up in many ways:
1. Calling InitializeFuzzingContext, which implicitly constructs a static
const BasicTestingSetup
2. Directly constructing a static const BasicTestingSetup in the initialize_*
function
3. Directly constructing a static TestingSetup and reproducing the
initialization arguments (I'm assuming because
InitializeFuzzingContext only initializes a BasicTestingSetup)
The new, relatively-simple MakeFuzzingContext function allows us to
consolidate these methods of initialization by being flexible enough to
be used in all situations. It:
1. Is templated so that we can choose to initialize any of
the *TestingSetup classes
2. Has sane defaults which are often used in fuzzers but are also
easily overridable
3. Returns a unique_ptr, explicitly transferring ownership to the caller
to deal with according to its situation
```
~~Question for fuzzing people: was it intentional that `src/test/fuzz/net.cpp` would directly instantiate the `BasicTestingSetup` and thus omit the `"-nodebuglogfile"` flag?~~ [Answered](https://github.com/bitcoin/bitcoin/pull/20946#issuecomment-761537108)
ACKs for top commit:
MarcoFalke:
ACK abb6fa728598c4cc8874eae1c3c5e587e36424cd
Tree-SHA512: 96a5ca6f4cd5ea0e9483b60165b31ae3e9003918c700a7f6ade48010f419f2a6312e10b816b3187f1d263798827571866e4c4ac0bbfb2e0c79dfad254cda68e7
85fee49c39