introduce constructing functions with typeassert for several types

Introduce functions to construct and typeassert several concrete types:

* `Bool`

* other primitive integers

* `Char`

* `String`

The new functions are meant to be used internally instead of the
original constructors to help inference.

Cross-reference issue #42372.

Author: nsajko

base/Base_compiler.jl

@@ -289,6 +289,7 @@ end
 setfield!(typeof(invoke_in_world).name, :max_args, Int32(3), :monotonic) # invoke_in_world, world, f, args...
 
 # core operations & types
+include("constructingfunctions.jl")
 include("promotion.jl")
 include("tuple.jl")
 include("expr.jl")

base/constructingfunctions.jl

@@ -0,0 +1,36 @@
+# Constructing functions for some concrete types.
+#
+# Meant to be used to improve inference, when the input arguments are not necessarily
+# precisely inferred. Partial workaround for issue #42372.
+module _ConstructingFunctions
+    export
+        _Bool,
+        _Int, _Int8, _Int16, _Int32, _Int64, _Int128,
+        _UInt, _UInt8, _UInt16, _UInt32, _UInt64, _UInt128,
+        _Char, _String
+    struct ConstructorStrict{F} <: Function end
+    # Keyword arguments are not available at this point in bootstrap, so they're not
+    # supported.
+    function (::ConstructorStrict{F})(args::Vararg{Any, N}) where {F, N}
+        @inline
+        r = F(args...)
+        r::F
+    end
+    const _Bool = ConstructorStrict{Bool}()
+    const _Int = ConstructorStrict{Int}()
+    const _Int8 = ConstructorStrict{Int8}()
+    const _Int16 = ConstructorStrict{Int16}()
+    const _Int32 = ConstructorStrict{Int32}()
+    const _Int64 = ConstructorStrict{Int64}()
+    const _Int128 = ConstructorStrict{Int128}()
+    const _UInt = ConstructorStrict{UInt}()
+    const _UInt8 = ConstructorStrict{UInt8}()
+    const _UInt16 = ConstructorStrict{UInt16}()
+    const _UInt32 = ConstructorStrict{UInt32}()
+    const _UInt64 = ConstructorStrict{UInt64}()
+    const _UInt128 = ConstructorStrict{UInt128}()
+    const _Char = ConstructorStrict{Char}()
+    const _String = ConstructorStrict{String}()
+end
+
+using ._ConstructingFunctions