resolves#2046
[Playround](https://cadlplayground.z22.web.core.windows.net/prs/3022/)
Add the new syntax for object literals using `#{`. For this first
version an object literal can only contain other object literal and
other literals(string, number, boolean))
## Values axioms
1. `alias` always produces a type. If you attempt to alias a value, you
get an error.
2. A string template produces a string template type if all
substitutions are types, and a value if all substitutions are numeric,
boolean, or string values. A mixture of types and values is an error.
3. The string literal syntax always results in a string literal type
4. A string literal type may be passed as a string value when the
signature expects a value. When the signature expects either a string
literal type or a string value, it is passed as a string value.
5. A string template type can be passed as a string value when all its
substitutions are string literal types.
## Breaking change
### Removal of the `ValueType` replacement with `MixedConstraint`
This shouldn't affect anyone as you were only exposed to this if you
digged into the template parameter and looked at the constraint
## Deprecation
## Using a tuple instead of a tuple literal
- ✅ still work
- emit a warning
<img width="1013" alt="image"
src="https://github.com/microsoft/typespec/assets/1031227/ab05359a-5ed9-4a27-a8d1-f40d1e21766f">
- provide a codefix
<img width="312" alt="image"
src="https://github.com/microsoft/typespec/assets/1031227/5ef93bdf-665f-4445-a6b2-62475efe8c16">
## Using a model expression instead of an object literal
This technically didn't work before(different from above where tuple was
used as a value) but allow this will allow us to convert most of our
decorators to use `valueof` without being breaking
## Old decorator marshalling
If a library had a decorator with `valueof` one of those types
`numeric`, `int64`, `uint64`, `integer`, `float`, `decimal`,
`decimal128`, `null` it used to marshall those as JS `number` and
`NullType` for `null`. With the introduction of values we have a new
marshalling logic which will marshall those numeric types as `Numeric`
and the others will remain numbers. `null` will also get marshalled as
`null`.
For now this is an opt-in behavior with a warning on decorators not
opt-in having a parameter with a constraint from the list above.
Example:
```
extern dec multipleOf(target: numeric | Reflection.ModelProperty, value: valueof numeric);
```
Will now emit a deprecated warning because `value` is of type `valueof
string` which would marshall to `Numeric` under the new logic but as
`number` previously.
To opt-in you can add the following to your library
```ts
export const $flags = defineModuleFlags({
decoratorArgMarshalling: "value",
});
```
---------
Co-authored-by: Brian Terlson <brian.terlson@microsoft.com>
Co-authored-by: Mark Cowlishaw <markcowl@microsoft.com>
Timothee Guerin