Add compat notes for Julia 1.6 (#39671)

(cherry picked from commit 715e626)

Author: sostock

base/cmd.jl

@@ -251,6 +251,9 @@ setenv(cmd::Cmd; dir="") = Cmd(cmd; dir=dir)
 Merge new environment mappings into the given `Cmd` object, returning a new `Cmd` object.
 Duplicate keys are replaced.  If `command` does not contain any environment values set already,
 it inherits the current environment at time of `addenv()` call if `inherit` is `true`.
+
+!!! compat "Julia 1.6"
+    This function requires Julia 1.6 or later.
 """
 function addenv(cmd::Cmd, env::Dict; inherit::Bool = true)
     new_env = Dict{String,String}()

base/floatfuncs.jl

@@ -253,6 +253,9 @@ for example, in `x - y ≈ 0`, `atol=1e-9` is an absurdly small tolerance if `x`
 but an absurdly large tolerance if `x` is the
 [radius of a Hydrogen atom](https://en.wikipedia.org/wiki/Bohr_radius) in meters.
 
+!!! compat "Julia 1.6"
+    Passing the `norm` keyword argument when comparing numeric (non-array) arguments
+    requires Julia 1.6 or later.
 
 # Examples
 ```jldoctest

base/operators.jl

@@ -1157,6 +1157,9 @@ Avoid adding methods to this function; define `in` instead.
 
 Create a function that checks whether its argument contains the given `item`, i.e.
 a function equivalent to `y -> item in y`.
+
+!!! compat "Julia 1.6"
+    This method requires Julia 1.6 or later.
 """
 ∋(x) = Fix2(∋, x)
 

base/strings/search.jl

@@ -628,6 +628,9 @@ Create a function that checks whether its argument occurs in `haystack`, i.e.
 a function equivalent to `needle -> occursin(needle, haystack)`.
 
 The returned function is of type `Base.Fix2{typeof(occursin)}`.
+
+!!! compat "Julia 1.6"
+    This method requires Julia 1.6 or later.
 """
 occursin(haystack) = Base.Fix2(occursin, haystack)
 

base/subarray.jl

@@ -135,6 +135,10 @@ Some immutable parent arrays (like ranges) may choose to simply
 recompute a new array in some circumstances instead of returning
 a `SubArray` if doing so is efficient and provides compatible semantics.
 
+!!! compat "Julia 1.6"
+    In Julia 1.6 or later, `view` can be called on an `AbstractString`, returning a
+    `SubString`.
+
 # Examples
 ```jldoctest
 julia> A = [1 2; 3 4]

stdlib/LinearAlgebra/src/dense.jl

@@ -347,6 +347,9 @@ overwriting the existing value of `C`.
 !!! tip
     Bounds checking can be disabled by [`@inbounds`](@ref), but you need to take care of the shape
     of `C`, `A`, `B` yourself.
+
+!!! compat "Julia 1.6"
+    This function requires Julia 1.6 or later.
 """
 @inline function kron!(C::AbstractMatrix, A::AbstractMatrix, B::AbstractMatrix)
     require_one_based_indexing(A, B)

stdlib/Printf/src/Printf.jl

@@ -56,6 +56,9 @@ formatted string directly to `io`.
 
 For convenience, the `Printf.format"..."` string macro form can be used for building
 a `Printf.Format` object at macro-expansion-time.
+
+!!! compat "Julia 1.6"
+    `Printf.Format` requires Julia 1.6 or later.
 """
 struct Format{S, T}
     str::S # original full format string as CodeUnits
@@ -375,6 +378,9 @@ For arbitrary precision numerics, you might extend the method like:
 ```julia
 Printf.tofloat(x::MyArbitraryPrecisionType) = BigFloat(x)
 ```
+
+!!! compat "Julia 1.6"
+    This function requires Julia 1.6 or later.
 """
 tofloat(x) = Float64(x)
 tofloat(x::Base.IEEEFloat) = x

stdlib/REPL/src/TerminalMenus/AbstractMenu.jl

@@ -149,6 +149,9 @@ keypress(m::AbstractMenu, i::UInt32) = false
     numoptions(m::AbstractMenu) -> Int
 
 Return the number of options in menu `m`. Defaults to `length(options(m))`.
+
+!!! compat "Julia 1.6"
+    This function requires Julia 1.6 or later.
 """
 numoptions(m::AbstractMenu) = length(options(m))
 
@@ -169,6 +172,9 @@ number used for the initial cursor position. `cursor` can be either an
 control of the cursor position from the outside.
 
 Returns `selected(m)`.
+
+!!! compat "Julia 1.6"
+    The `cursor` argument requires Julia 1.6 or later.
 """
 request(m::AbstractMenu; kwargs...) = request(terminal, m; kwargs...)
 

stdlib/REPL/src/TerminalMenus/MultiSelectMenu.jl

@@ -51,6 +51,9 @@ were selected by the user.
   - `selected=[]`: pre-selected items. `i ∈ selected` means that `options[i]` is preselected.
 
 Any additional keyword arguments will be passed to [`TerminalMenus.MultiSelectConfig`](@ref).
+
+!!! compat "Julia 1.6"
+    The `selected` argument requires Julia 1.6 or later.
 """
 function MultiSelectMenu(options::Array{String,1}; pagesize::Int=10, selected=Int[], warn::Bool=true, kwargs...)
     length(options) < 1 && error("MultiSelectMenu must have at least one option")