Add tooltips/hover text to Library Symbol Properties window explaining "Has alternate body design" and "All units are interchangeable"

Description

Interchangable? Alternate body design? Place polygon in place menu?

Steps to reproduce

1. In the Symbol Editor window, click in white space.
2. Press 'E' on your keyboard to open the "Library Symbol Properties" window.
3. Hover over the "Has alternate body design" and "All units are interchangeable" fields.
4. Observe that there is no hover text explaining what these buttons do.

Please add hover text explaining what they do.

KiCad Version

Application: KiCad Symbol Editor x64 on x64

Version: 7.0.1, release build

Libraries:
	wxWidgets 3.2.2
	FreeType 2.12.1
	HarfBuzz 5.0.1
	FontConfig 2.14.1
	libcurl/7.83.1-DEV Schannel zlib/1.2.13

Platform: Windows 10 (build 19044), 64-bit edition, 64 bit, Little endian, wxMSW

Build Info:
	Date: Mar 11 2023 03:41:46
	wxWidgets: 3.2.2 (wchar_t,wx containers)
	Boost: 1.80.0
	OCC: 7.6.2
	Curl: 7.83.1-DEV
	ngspice: 39
	Compiler: Visual C++ 1934 without C++ ABI

Build settings:
	KICAD_SPICE=ON