Somehow it slipped #1695

<details><summary>Contributors' checklist...</summary>

- [x] Added new tests, or not needed, or not feasible
- [x] Provided an example (e.g. screenshot) to aid review or the PR is
self-explanatory
- [x] Updated the official documentation or not needed
- [x] No breaking changes were made, or a `BREAKING CHANGE: xxx` message
was included in the description
- [x] Added references to related issues and PRs
- [x] Provided any useful hints for running manual tests
- [x] Added new benchmarks to [generated
graphs](https://gnoland.github.io/benchmarks), if any. More info
[here](https://github.com/gnolang/gno/blob/master/.benchmarks/README.md).
</details>

Merge order:

1. gnolang#1700 
2. gnolang#1702
3. gnolang#1695 (this one!) -- review earlier ones first, if they're still
open!

This PR modifies the Gno transpiler (fka precompiler) to use Gno's
standard libraries rather than Go's when performing transpilation. This
creates the necessity to transpile Gno standard libraries, and as such
support their native bindings. And it removes the necessity for a
package like `stdshim`, and a mechanism like `stdlibWhitelist`.

- Fixes gnolang#668. Fixes gnolang#1865.
- Resolves gnolang#892.
- Part of gnolang#814. 
- Makes gnolang#1475 / gnolang#1576 possible without using hacks like `stdshim`.

cc/ @leohhhn @tbruyelle, as this relates to your work

## Why?

- This PR enables us to perform Go type-checking across the board, and
not use Go's standard libraries in transpiled code. This enables us to
_properly support our own standard libraries_, such as `std` but any
others we might want or need.
- It also paves the way further to go full circle, and have Gno code be
transpiled to Go, and then have "compilable" gno code

## Summary of changes

- The transpiler has been thoroughly refactored.
- The biggest change is described above: instead of maintaing the import
paths like `"strconv"` and `"math"` the same (so using Gno's stdlibs in
Gno, and Go's in Go), the import paths for standard libraries is now
also updated to point to the Gno standard libraries.
- Native functions are handled by removing their definitions when
transpiling, and changing their call expressions where appropriate. This
links the transpiled code directly to their native counterparts.
  - This removes the necessity for `stdlibWhitelist`. 
- As a consequence, `stdshim` is no longer needed and has been removed.
- Test files are still not "strictly checked": they may reference
stdlibs with no matching source, and will not be tested when running
with `--gobuild`. This is because packages like `fmt` have no
representation in Gno code; they only exist as injections in
`tests/imports.go`. I'll fix this eventually :)
- The CLI (`gno transpile`) has been changed to reflect the above
changes.
- Flag `--skip-fmt` has been removed (the result of transpile is always
formatted, anyway), and `--gofmt-binary` too, obviously. `gno transpile`
does not perform validation, but will gladly provide helpful validation
with the `--gobuild` flag.
- There is another PR that adds type checking in `gno lint`, without
needing to run through the transpilation step first:
gnolang#1730
- It now works by default by looking at "packages" rather than
individual files. This is necessary so that when performing `transpile`
on the `examples` directory, we can skip those where the gno.mod marks
the module as draft. These modules make use of packages like "fmt",
which because they don't have an underlying gno/go source, cannot be
transpiled.
- Running with `-gobuild` now handles more errors correctly; ie., all
errors not previously captured by the `errorRe` which only matches those
pertaining to a specific file/line.
  - `gnoFilesFromArgs` was unused and as such deleted
- `gnomod`'s behaviour was slightly changed.
- I am of the opinion that `gno mod download` should not precompile what
it downloads; _especially_ to gather the dependencies it has. I've
changed it so that it does a `OnlyImports` parse of the file it
downloads to fetch additional dependencies

Misc:

- `Makefile` now contains a recipe to calculate the coverage for
`gnovm/cmd/gno`, and also view it via the HTML interface. This is needed
as it has a few extra steps (which @gfanton already previously added in
the CI).
- Realms r/demo/art/gnoface and r/x/manfred_outfmt have been marked as
draft, as they depend on packages which are not actually present in the
Gno standard libraries.
  - The transpiler now ignores draft packages by default.
- `ReadMemPackage` now also considers Go files. This is meant to have
on-chain the code for standard libraries like `std` which have native
bindings. We still exclude Go code if it's not in a standard library.
- `//go:build` constraints have been removed from standard libraries, as
go files can only have one and we already add our own when transpiling

## Further improvements

after this PR

- Scope understanding in `transpiler` (so call expressions are not
incorrectly rewritten)
- Correctly transpile gno.mod

---------

Co-authored-by: Antonio Navarro Perez <antnavper@gmail.com>
Co-authored-by: Miloš Živković <milos.zivkovic@tendermint.com>

Somehow it slipped gnolang#1695

<details><summary>Contributors' checklist...</summary>

- [x] Added new tests, or not needed, or not feasible
- [x] Provided an example (e.g. screenshot) to aid review or the PR is
self-explanatory
- [x] Updated the official documentation or not needed
- [x] No breaking changes were made, or a `BREAKING CHANGE: xxx` message
was included in the description
- [x] Added references to related issues and PRs
- [x] Provided any useful hints for running manual tests
- [x] Added new benchmarks to [generated
graphs](https://gnoland.github.io/benchmarks), if any. More info
[here](https://github.com/gnolang/gno/blob/master/.benchmarks/README.md).
</details>