This is the first part of the major section going over custom
widgets and the general widget model.

Co-Authored-By: Leopold Luley <git@leopoldluley.de>

Keep hot state consistent with mouse position.

* Add wasm backend + fix std::time dep

A basic wasm backend is added as a continuation of #30.
Since std::time isn't available on wasm, an additional dependency is
added to abstract std::time::Instant to work with wasm.

* Disable simple logger on wasm

This commit ensures that all examples run with minimal changes.
More specifically we don't need to remove the .use_simple_logger() call
on all Apps.

* Fix resizing in wasm backends

The resize callback should be registered to the window, since resizing
the window doesn't call the resize callback for canvases even if those
do get resized.

* Added scrolling support + fixed hidpi handling

The scroll example now works as expected on hi and low dpi screens.

* Use explicit lifetime in StrOrChar

This makes passing it easier to pass owned strings when creating a new
KeyEvent, which is necessary when interfacing with WASM.

* Prevent the browser from going back on backspace

This should be the default behavior to make text widgets usable.
At a later iteration it may be better to only disable the browser from
going back when a widget is selected that is expecting keyboard input
where backspace is intended for something else.

I expect this functionality would require some way of accessing the
web_sys event from within a druid callback.

* Fix key text + require console_log + adjust style

This commit addresses comments in the code review:

Key text:
  - web_sys returns the name of each pressed key from which we can
    generate a viable printable string. This mechanism is revised to
    include all non-printable keys as listed in MDN.
  - notably, the tab character and numpad characters have gained
    printable text in this commit.

console_log:
  - console_log is not required in wasm builds.
  - integrated console_log with the use_simple_logger api. `console_log`
    is initialized with log level `trace` as is done in simple logger by
    default.

Style:
  - non std use statements are now before third party use statements.
  - key_to_text function signature refactor
  - specify the log module when calling log::{warn, error} explicitly.

* Fix up console_log dependency

Moved console_log dependency from druid-shell to druid, since this is
where it is initialized. This fixes the wasm build.

* Fix the build script for wasm examples

This addresses the CI failures caused by the weird build of the wasm
examples.

To elaborate:
In order to include each of the examples in the wasm example, a
symlink to the examples directory is created in build.rs along with the
corresponding examples.rs module which declares examples known to work
with wasm. To satisfy CI, the examples.rs committed to the repo must be
empty since rustfmt does not call "build.rs".

* Add .gitignore to wasm examples + fix clippy bugs

The included .gitignore ignores the generated examples module. The
examples.rs should remain committed, but it need not be ever changed.

* Fix x11 keycodes StrOrChar conversion

The newly introduced lifetime parameter must be specified exmplicitly.


* Add --no-run to `cargo test` for wasm targets

wasm targets cannot be run in the normal way.

* Do not build the unit test module for wasm32

The tests cannot be run in the normal way anyways. Leaving this for a
future PR to flush out.

* Install necessary deps in wasm CI for macos/ubuntu

* Add warnings for unimplemented file ops in web backend

This commit exposes the error of the missing implementation for file dialogs in the web backend using log::warn. This is a temporary solution until the `open_file_sync` and `save_as_sync` functions propagate the error downstream using Result instead of Option.

* Rework the generated examples in the wasm example

This commit attempts a different approach at including the automatically
generated examples from the parent directory.
This method satisfies both rustfmt and cargo test as before, but it also
doesn't modify any files in the source tree, keeping the diff clean
after a build.

* Rename switch example js entry point for wasm build

This commit fixes the generated html file for the switch example to load
"switch_demo" instead of "switch" for the switch example. The word
switch conflicts with JavaScript's switch statement, which is the reason
for this awkwardness.

Co-authored-by: Leopold Luley <git@leopoldluley.de>