vim-patch:8.2.0155: MinGW warnings; tests without +float #15908

Problem:    Warnings from MinGW compiler. (John Marriott) Json test fails when
            building without +float feature.
Solution:   Init variables. Fix Json parsing. Skip a few tests that require
            the +float feature.
a5d5953d59

Omit vim9 changes.
vim9 internal implementation is N/A,
similar to the `vimscript-*` features.

N/A patches for version.c:

vim-patch:8.1.0737: compiler warning for uninitialized variable

Problem:    Compiler warning for uninitialized variable.
Solution:   Add initialization. (John Marriott)
e519dfd713

vim-patch:8.1.1385: signed/unsigned compiler warning

Problem:    Signed/unsigned compiler warning.
Solution:   Use STRLEN() instead of strlen().
71de720c2c

vim-patch:8.2.0165: Coverity warning for using NULL pointer

Problem:    Coverity warning for using NULL pointer.
Solution:   Add missing "else".
5b18c248d3

vim-patch:8.2.0166: Coverity warning for using uninitialized variable

Problem:    Coverity warning for using uninitialized variable.
Solution:   Check for failure.
07da94b0f0

vim-patch:8.2.0167: Coverity warning for ignoring return value

Problem:    Coverity warning for ignoring return value.
Solution:   Check the return value and jump if failed.
58ceca5cae

"src/testdir/test_vim9*.vim" files are N/A
because vim9 code is currently unsupported.

vim-patch:8.2.0168: Coverity warning for assigning NULL to an option

Problem:    Coverity warning for assigning NULL to an option.
Solution:   Use empty string instead of NULL.
97a2af39cd

vim-patch:8.2.0169: Coverity warning for dead code

Problem:    Coverity warning for dead code.
Solution:   Check if inside try-finally.
8cbd6dfc0c

vim-patch:8.2.0170: Coverity warning for ignoring return value

Problem:    Coverity warning for ignoring return value.
Solution:   Check the return value and return if failed.
a6d536829a

vim-patch:8.2.0172: Coverity warning for not restoring character

Problem:    Coverity warning for not restoring character.
Solution:   Restore the character also in case of failure.
4549ece47c

vim-patch:8.2.0254: compiler warning for checking size_t to be negative

Problem:    Compiler warning for checking size_t to be negative.
Solution:   Only check for zero. (Zoltan Arpadffy)
ae8d2de3a9

vim-patch:8.2.0326: compiler warning for using uninitialized variable

Problem:    Compiler warning for using uninitialized variable. (Yegappan
            Lakshmanan)
Solution:   Do not jump to failed but return.
d5aec0ced1

vim-patch:8.2.3387: compiler warning for non-static function

Problem:    Compiler warning for non-static function.
Solution:   Make the function static. (Dominique Pellé, closes vim/vim#8816)
de05ae7158

src/nvim/testdir/test_method.vim

@@ -1,5 +1,7 @@
 " Tests for ->method()
 
+source check.vim
+
 func Test_list_method()
   let l = [1, 2, 3]
   call assert_equal([1, 2, 3, 4], [1, 2, 3]->add(4))
@@ -118,6 +120,7 @@ func Test_method_funcref()
 endfunc
 
 func Test_method_float()
+  CheckFeature float
   eval 1.234->string()->assert_equal('1.234')
   eval -1.234->string()->assert_equal('-1.234')
 endfunc