Only call text_layout once in getmask2

[radarhere]

Helps #6618

Backstory
The following is an earlier version of ImageFont's getmask2(), as described in the quoted comment.

Pillow/src/PIL/ImageFont.py

Lines 752 to 777 in 3cfdef3

	if fill is _UNSPECIFIED:
	fill = Image.core.fill
	else:
	deprecate("fill", 10)
	size, offset = self.font.getsize(
	text, mode, direction, features, language, anchor
	)
	if start is None:
	start = (0, 0)
	size = tuple(math.ceil(size[i] + stroke_width * 2 + start[i]) for i in range(2))
	offset = offset[0] - stroke_width, offset[1] - stroke_width
	Image._decompression_bomb_check(size)
	im = fill("RGBA" if mode == "RGBA" else "L", size, 0)
	if min(size):
	self.font.render(
	text,
	im.id,
	mode,
	direction,
	features,
	language,
	stroke_width,
	ink,
	start[0],
	start[1],
	)

#6618 (comment)

The function getmask2 performs the following steps:

1. calls getsize to get the size of the text
2. calls Image._decompression_bomb_check to compare size with MAX_IMAGE_PIXELS
3. calls the fill function passed as argument to create a blank image
4. calls render to draw text into the blank image

After Pillow 10 the deprecated fill parameter will be replaced by a direct call to the internal function. After this, the only Python function to be called between the two C functions is the decompression bomb check. If this was moved into C, the two functions could be combined to remove the duplicate call to text_layout.

#7059 removed the deprecated fill parameter. So here is the current version of ImageFont's getmask2().

Pillow/src/PIL/ImageFont.py

Lines 554 to 575 in 1fc8d82

	size, offset = self.font.getsize(
	text, mode, direction, features, language, anchor
	)
	if start is None:
	start = (0, 0)
	size = tuple(math.ceil(size[i] + stroke_width * 2 + start[i]) for i in range(2))
	offset = offset[0] - stroke_width, offset[1] - stroke_width
	Image._decompression_bomb_check(size)
	im = Image.core.fill("RGBA" if mode == "RGBA" else "L", size, 0)
	if min(size):
	self.font.render(
	text,
	im.id,
	mode,
	direction,
	features,
	language,
	stroke_width,
	ink,
	start[0],
	start[1],
	)

This is the only place that font.render is called.

Change
So I added a change to make font.getsize a builtin part of font.render, meaning that text_layout is not called once by each, but only once.

From my tests, this causes getmask2 to be 10% faster.

There is an awkward part of this change though - the _imagingft extension is not connected to the C code for creating new images. I couldn't call ImagingNewDirty and ImagingFill. Despite the quoted comment's expectation that this could all be done in C, it didn't realise that our C code is actually split up into these extensions. Instead, I've passed Image.core.fill into C, to then be called by PyObject_CallFunction.