* accounts/abi: fix name styling when unpacking abi fields w/ underscores

ABI fields with underscores that are being unpacked
into structs expect structs with following form:

int_one -> Int_one

whereas in abigen the generated structs are camelcased

int_one -> IntOne

so updated the unpack method to expect camelcased structs as well.

Go code users can now tag event struct members with `abi:` to specify in what fields the event will be de-serialized.

See PR #16648 for details.

+ The event slice unpacker doesn't correctly extract element from the
slice. The indexed arguments are not ignored as they should be
(the data offset should not include the indexed arguments).

+ The `Elem()` call in the slice unpack doesn't work.
The Slice related tests fails because of that.

+ the check in the loop are suboptimal and have been extracted
out of the loop.

+ extracted common code from event and method tupleUnpack

* accounts/abi: reorganizing package and some notes and a quick correction of name.
Signed-off-by: NRJ Catalano <rj@monax.io>

get rid of some imports
Signed-off-by: NRJ Catalano <rj@monax.io>

* accounts/abi: move file names
Signed-off-by: NRJ Catalano <rj@monax.io>

* accounts/abi: fix boolean decode function
Signed-off-by: NRJ Catalano <rj@monax.io>

* accounts/abi: fix for the array set and for creating a bool
Signed-off-by: NRJ Catalano <rj@monax.io>

* accounts/abi: be very very very correct
Signed-off-by: NRJ Catalano <rj@monax.io>

* accounts/abi: fix up error message and variable names
Signed-off-by: NRJ Catalano <rj@monax.io>

* accounts/abi: take out unnecessary argument in pack method
Signed-off-by: NRJ Catalano <rj@monax.io>

* accounts/abi: add bool unpack test and add a panic to readBool function
Signed-off-by: NRJ Catalano <rj@monax.io>

* accounts/abi: fix panic message
Signed-off-by: NRJ Catalano <rj@monax.io>

* accounts/abi: change from panic to basic error
Signed-off-by: NRJ Catalano <rj@monax.io>

* accounts/abi: fix nil to false
Signed-off-by: NRJ Catalano <rj@monax.io>

* accounts/abi: fill out type regex tests and fill with the correct type for integers
Signed-off-by: NRJ Catalano <rj@monax.io>

* accounts/abi: move packNumbers into pack.go.
Signed-off-by: NRJ Catalano <rj@monax.io>

* accounts/abi: separation of the testing suite into appropriately named files.
Signed-off-by: NRJ Catalano <rj@monax.io>

* account/abi: change to hex string tests.
Signed-off-by: NRJ Catalano <rj@monax.io>

* account/abi: fix up rest of tests to hex
Signed-off-by: NRJ Catalano <rj@monax.io>

* accounts/abi: declare bool at the package level
Signed-off-by: NRJ Catalano <rj@monax.io>

* accounts/abi: use errors package in the error file.
Signed-off-by: NRJ Catalano <rj@monax.io>

* accounts/abi: fix ugly hack and fix error type declaration.
Signed-off-by: NRJ Catalano <rj@monax.io>

solves #3119
Signed-off-by: NVoR0220 <rj@erisindustries.com>

Previously it was assumed that wheneven type `[]interface{}` was given
that the interface was empty. The abigen rightfully assumed that
interface slices which already have pre-allocated variable sets to be
assigned.

This PR fixes that by checking that the given `[]interface{}` is larger
than zero and assigns each value using the generic `set` function (this
function has also been moved to abi/reflect.go) and checks whether the
assignment was possible.

The generic assignment function `set` now also deals with pointers
(useful for interface slice mentioned above) by dereferencing the
pointer until it finds a setable type.

Refactored the abi package parsing and type handling. Relying mostly on
package reflect as opposed to most of our own type reflection. Our own
type reflection is still used however for cases such as Bytes and
FixedBytes (abi: bytes•).

This also inclused several fixes for slice handling of arbitrary and
fixed size for all supported types.

This also further removes implicit type casting such as assigning,
for example `[2]T{} = []T{1}` will fail, however `[2]T{} == []T{1, 2}`
(notice assigning *slice* to fixed size *array*). Assigning arrays to
slices will always succeed if they are of the same element type.

Incidentally also fixes #2379