Previously, there was a single parsing rule for "bare words" that
applied to both internal and external commands.
This meant that, because `cargo +nightly` needed to work, we needed to
add `+` as a valid character in bare words.
The number of characters continued to grow, and the situation was
becoming untenable. The current strategy would eventually eat up all
syntax and make it impossible to add syntax like `@foo` to internal
commands.
This patch significantly restricts bare words and introduces a new token
type (`ExternalWord`). An `ExternalWord` expands to an error in the
internal syntax, but expands to a bare word in the external syntax.
`ExternalWords` are highlighted in grey in the shell.
Fixes#627
Fixes a regression caused by #579, specifically commit cc8872b4ee .
The code was intended to perform a comparison between the wanted
output type and "Tagged<Value>" in order to be able to provide a
special-cased path for Tagged<Value>. When I wrote the code, I
used "name" as a variable name and only later realized that it
shadowed the "name" param to the function, so I renamed it to
type_name, but forgot to change the comparison.
This broke the special-casing, as the name param only contains
the name of the struct without generics (like "Tagged"), while
`std::any::type_name` (in the current implementation) contains
the full paths of the struct including all generic params
(like "nu::object::meta::Tagged<nu::object::base::Value>").
At the moment the pipeline parser does not enforce
that there must be a pipe between each part of the pipeline,
which can lead to confusing behaviour or misleading errors.
