Fix error message when using const inside a function, require the LHS to be global, and prohibit "const x[] = 1"

[xal-0]

The changes to const resulted in confusing error messages when it was used
inside a function (#57334). On 1.11.3:

julia> function f()
           const x = 1
       end
ERROR: syntax: unsupported `const` declaration on local variable around REPL[1]:2
Stacktrace:
 [1] top-level scope
   @ REPL[1]:1

On nightly:

julia> function f()
           const x = 1
       end
ERROR: syntax: World age increment not at top level
Stacktrace:
 [1] top-level scope
   @ REPL[1]:1

In prior versions, we also accepted confused expressions like:

x = Ref(1)
const x[] = 1

This change adds a new error messages explicitly prohibiting const where the
left hand side is not declaring variables:

ERROR: syntax: `const` left hand side "x[]" contains non-variables around REPL[2]:1
Stacktrace:
 [1] top-level scope
   @ REPL[2]:1

Finally, #54773 made const stop participating in scope resolution (the left
hand side was always taken to be in global scope). Some expressions that were
prohibited started being accepted:

In 1.11.3:

julia> let
           const x = 1
       end
ERROR: syntax: unsupported `const` declaration on local variable around REPL[1]:2
Stacktrace:
 [1] top-level scope
   @ REPL[1]:1

Nightly:

julia> let
           const x = 1
       end
1

This change rejects const unless the variable would be in global scope
(global const would be required in the example), so we don't lose the
ability to make const in local scope meaningful later.

[vtjnash]

LGTM. Minor nit with this error though:

julia> const (x{T},) = T
ERROR: syntax: `const` left hand side "SSAValue(81)" contains non-variables around REPL[13]:1

[xal-0]

Argh, this is actually a regression.

1.11.3:

julia> const X{T}, Y{U} = [Int, Int]
2-element Vector{DataType}:
 Int64
 Int64

This:

julia> const X{T}, Y{U} = [Int, Int]
ERROR: syntax: `const` left hand side "SSAValue(4)" contains non-variables around REPL[1]:1
Stacktrace:
 [1] top-level scope
   @ REPL[1]:1

I'll need to think of a way to handle this.