BigFloat: Print exponent without leading '+' and zeros (#58008)

Fixes #56941

With this small change we get:
```julia
julia> big"1e6"
1.0e6
```

Author: pjaap

base/mpfr.jl

@@ -1229,7 +1229,7 @@ function _prettify_bigfloat(s::String)::String
             string(neg ? '-' : "", '0', '.', '0'^(-expo-1), int, frac == "0" ? "" : frac)
         end
     else
-        string(mantissa, 'e', exponent)
+        string(mantissa, 'e', expo)
     end
 end
 

doc/src/manual/integers-and-floating-point-numbers.md

@@ -600,7 +600,7 @@ julia> parse(BigFloat, "1.23456789012345678901")
 1.234567890123456789010000000000000000000000000000000000000000000000000000000004
 
 julia> BigFloat(2.0^66) / 3
-2.459565876494606882133333333333333333333333333333333333333333333333333333333344e+19
+2.459565876494606882133333333333333333333333333333333333333333333333333333333344e19
 
 julia> factorial(BigInt(40))
 815915283247897734345611269596115894272000000000

test/mpfr.jl

@@ -667,16 +667,19 @@ end
         @test string(parse(BigFloat, "0.1")) == "0.10000002"
         @test string(parse(BigFloat, "0.5")) == "0.5"
         @test string(parse(BigFloat, "-9.9")) == "-9.9000015"
+        @test string(parse(BigFloat, "1e6")) == "1.0e6"
     end
     setprecision(40) do
         @test string(parse(BigFloat, "0.1")) == "0.10000000000002"
         @test string(parse(BigFloat, "0.5")) == "0.5"
         @test string(parse(BigFloat, "-9.9")) == "-9.8999999999942"
+        @test string(parse(BigFloat, "1e6")) == "1.0e6"
     end
     setprecision(123) do
         @test string(parse(BigFloat, "0.1")) == "0.0999999999999999999999999999999999999953"
         @test string(parse(BigFloat, "0.5")) == "0.5"
         @test string(parse(BigFloat, "-9.9")) == "-9.8999999999999999999999999999999999997"
+        @test string(parse(BigFloat, "1e6")) == "1.0e6"
     end
 end
 @testset "eps" begin
@@ -998,18 +1001,18 @@ end
 
     test_show_bigfloat(big"1.23456789", contains_e=false, starts="1.23")
     test_show_bigfloat(big"-1.23456789", contains_e=false, starts="-1.23")
-    test_show_bigfloat(big"2.3457645687563543266576889678956787e10000", starts="2.345", ends="e+10000")
+    test_show_bigfloat(big"2.3457645687563543266576889678956787e10000", starts="2.345", ends="e10000")
     test_show_bigfloat(big"-2.3457645687563543266576889678956787e-10000", starts="-2.345", ends="e-10000")
     test_show_bigfloat(big"42.0", contains_e=false, starts="42.0")
     test_show_bigfloat(big"420.0", contains_e=false, starts="420.0") # '0's have to be added on the right before point
     test_show_bigfloat(big"-420.0", contains_e=false, starts="-420.0")
     test_show_bigfloat(big"420000.0", contains_e=false, starts="420000.0")
     test_show_bigfloat(big"654321.0", contains_e=false, starts="654321.0")
     test_show_bigfloat(big"-654321.0", contains_e=false, starts="-654321.0")
-    test_show_bigfloat(big"6543210.0", contains_e=true, starts="6.5", ends="e+06")
+    test_show_bigfloat(big"6543210.0", contains_e=true, starts="6.5", ends="e6")
     test_show_bigfloat(big"0.000123", contains_e=false, starts="0.000123")
     test_show_bigfloat(big"-0.000123", contains_e=false, starts="-0.000123")
-    test_show_bigfloat(big"0.00001234", contains_e=true, starts="1.23", ends="e-05")
+    test_show_bigfloat(big"0.00001234", contains_e=true, starts="1.23", ends="e-5")
 
     for to_string in [string,
                       x->sprint(show, x),